Beamer

One keyboard and one mouse or trackpad for Macs, Windows PCs and Linux machines on the same network, in either direction.

Push the pointer off the edge of the screen and it carries on onto the other machine, the way it would onto a second monitor. Or double-tap a key. The clipboard comes with you, your shortcuts still work, and what you type never leaves your network.

Download

Free, with no account. Mac and Windows downloads, and an experimental Linux Flatpak, are on the releases page.

Platform	Get it	Notes
macOS 13 or later, Apple silicon or Intel	Beamer-<version>.dmg	One universal app, signed and notarised by Apple
Windows 10 and 11	Beamer-Setup-<version>.exe	Not code-signed; see step 1 below
Linux, through Flatpak (experimental)	Beamer-<version>-x86_64.flatpak, or build it with the Linux instructions	GNOME on Wayland, or X11; tested on one GNOME Wayland desktop

Quick start

1. Install on every machine. On the Mac, drag Beamer to Applications, open it, and press the two Grant buttons on the Permissions page (Accessibility, then Input Monitoring), then Relaunch Beamer on the same page: macOS only passes keys to an app started after the grant, so until then the pointer crosses but the keyboard does not. On Windows, run the installer. It is not code-signed, because a certificate costs money and Beamer is free, so Windows says "Windows protected your PC" the first time: choose More info, then Run anyway. Beamer on Windows runs as administrator, so expect one UAC prompt when you open it. On Linux, install the Flatpak with flatpak install --user Beamer-<version>-x86_64.flatpak, or build it with the Flatpak instructions.
2. Pair them. On one machine, choose Pair a machine to show a six-digit code. On the other, choose that machine from the list and enter the code. It lasts a minute and works once. If it does not appear in the list, enter the address shown with its code on the other machine.
3. Cross. Push the pointer through the edge you set, or use the shortcut. On Wayland, an edge sends input out and the shortcut brings it back. The other machine's keyboard and pointer come with it. Cross back through the edge or use the shortcut again.

That is all most people need. The edge, the keys and everything else can be changed in each machine's settings.

Screenshots

In your own appearance: light if your GitHub is light, dark if it is dark.

Mac	Windows

What it does

• Push through the edge. Off the edge that faces the other machine, only along the parts of it you pick, through a corner, or up through the MacBook's notch. The pointer arrives at the same point along the border, on the right display however your monitors are stacked or staggered. The edge lights up as you push, and the trackpad ticks as the push builds. If Windows or macOS briefly cannot report the pointer position, Beamer skips that moment and keeps crossing (GitHub #9).
• See where you land. A switch by the key or a menu plays a short arrival around the pointer on the machine that takes over, so you never hunt for it.
• Or press a key. Double-tap or hold a trigger key to switch without moving the pointer. Right Option on the Mac and Right Ctrl on the PC to start with; on either machine it can be any key that types nothing, recorded by pressing it.
• Either way round. The Mac drives the PC and the PC drives the Mac. Each machine has a switch per direction, so you can turn one way off and keep the other. Macs can drive Macs, and Windows PCs can drive Windows PCs, too.
• Pair them clearly. Pair a machine is at the top of Overview, and the six digits are centred.
• Three machines. Pair each machine with the others in the group. A chain needs a direct pairing between every pair of machines in it.
• The clipboard comes with you. Text and images, both ways, at the moment you switch. Files stay where they are.
• Your shortcuts still work. Between a Mac and Windows, Cmd becomes Ctrl and Option becomes Alt, so Cmd+C copies there too. The PC gets the reverse. Between two Macs or two PCs, each key arrives as the same physical key. On Windows, you can also choose a Mac keyboard layout, where Alt acts as Command and the Windows key acts as Option.
• Media keys follow you. Play, pause, skip, mute and volume cross between supported machines. Brightness and keyboard-backlight keys stay on the Mac.
• Keys and buttons that stay put. Each machine keeps a list of keys and mouse buttons that keep working where they were pressed while its input is on the other one: a mouse's back button for this machine's browser, a volume key for its speakers. Add one by pressing it. The back and forward side buttons cross in both directions otherwise.
• Mac gestures on Windows. Three or four fingers up for Task View, down for the desktop, left and right to change virtual desktop, all from the Mac's trackpad.
• Make it yours. Glow, Beam and Aperture, or effects in Membrane, Sparks, Instrument, Folio and Selvedge, each with colour packs of its own. Set the effect's Size and Length, the MacBook notch as an outline or an island with a meter, how hard you push before it crosses, and whether settings windows follow the system's light or dark appearance. Beam fades softly inward from the edge.
• Feels like your own. Each machine sets how the other's pointer moves and scrolls on it, from 25% to 400%, and can reverse its scrolling, so a Mac trackpad and a PC mouse each feel right on the other screen.
• Out of the way when it should be. On macOS and Windows, you can choose whether a full-screen app on each machine holds its edges; it is off by default, and shortcuts still work. A drag that reaches the edge stays a drag. Switch to a machine that is asleep and Beamer wakes it, where that machine answers wake-on-LAN: a PC usually does, a MacBook on Wi-Fi usually does not.
• Keep settings in step. Same on all machines shares resistance, drag protection, Shortcut, effect style, colour, length, size and landing animation with compatible paired machines. Zones, jump keys, full-screen hold, whether effects animate, and window appearance stay local.
• Match design. Follow one paired machine's style, colour, length, size and landing animation. Changing one of those here stops following. Animation enable and window appearance stay local.
• A more responsive settings window. Mac resizing and scrolling stay smooth, the Design grid fills the window, and Windows and Linux settings layouts use their space more clearly.
• Your network, nobody else's. No server in the middle. Paired machines talk to each other directly, encrypted, and you pair them once with a six-digit code. The only thing that ever goes further is a once-a-day check of GitHub's public releases for a newer version, which you can switch off on Overview. More in SECURITY.md.
• Free and open source. No account, no subscription, GPL-3.0.

Settings

Each machine has its own settings window and makes its own choices about how input leaves it. Both sidebars end with the version and a link to kalkmancode.co.uk/beamer, and both menus have About Beamer.

Page	Mac	Windows
Overview	Paired machines, where input is, the links and their round trips, Send input and Pause crossing, a switch per direction, Same on all machines, start at login, the update check	Paired machines, where input is, the links and their round trips, Send input and Pause crossing, a switch per direction, Same on all machines, start at sign-in, the update check
Permissions	Accessibility and Input Monitoring, with Relaunch Beamer	None; the firewall check is on Connection
Crossing	A drawing of the arrangement, the ways in for each machine (edge, part of the edge, corner, notch), the full-screen hold, resistance, the shortcut and jump keys	A drawing of the arrangement, the ways in for each machine (edge, part of the edge, corner), the full-screen hold, resistance, the shortcut and jump keys
Keyboard	Key mapping, what stays on this Mac, each peer's pointer and scroll speed	Key mapping, including a Mac layout, what stays on this PC, each peer's pointer and scroll speed
Design	Crossing and switch styles, colours, Size and Length, landing animation, Match design, notch and trackpad controls, window appearance (System, Light or Dark)	Crossing and switch styles, colours, Size and Length, landing animation, Match design, window appearance (System, Light or Dark)
Connection	Hide addresses, a peer's address, port and pairing details	Whether Windows Firewall lets a peer in, with a one-button fix; hide addresses; this PC's address, port and pairing details

Each machine sets its own zones and the machine beyond each one. These settings stay local even when Same on all machines is on.

Known limits

• The Windows secure desktop cannot be driven. UAC prompts, Ctrl+Alt+Del and the lock screen refuse input from any app by design, and Ctrl+Alt+Del cannot be sent at all. Use the PC's own keyboard there.
• Files do not cross, only text and images, up to 256KB of text and an 8MB image.
• AltGr is out of reach from the Mac.
• Linux on Wayland has fewer controls. Its limits are listed under Linux.
• Linux gestures are not supported.
• The Windows installer is unsigned. SmartScreen may warn when you first run it; choose More info, then Run anyway.

In detail

Connection states

These examples use a Mac connected to a Windows PC. Beamer names the other machine in each status, and reports the mirror status at the other end.

Status	Meaning
Connected to <address>:<port>	The encrypted link is up and the protocol versions match.
<machine> is reachable, but Beamer is not listening on this port.	The other machine answered but nothing accepted the TCP port.
<machine> could not be authenticated — check the shared token matches on both sides	The two derived different keys. The tokens differ.
<machine> is unreachable from this Mac	Nothing got as far as Beamer or the firewall. Check Wi-Fi client isolation, the other machine's network, and that the Mac can resolve its address.
<machine> did not answer the handshake — it is probably running an older Beamer; update it	An older Beamer may not understand the current connection.
<machine> speaks Beamer protocol vN, this machine vM — update both apps	The wire versions differ. The version travels in cleartext at the start of the connection, so a mismatch says so rather than hanging.
<machine> stopped responding	No ping or acknowledgement for about two seconds.

Both ends notice a dead link within a few seconds. The receiver enforces a read timeout and the sender pings while idle; the machine holding input takes it back when the link is lost.

A dropped connection, a missing acknowledgement, a crashed capture worker or a full event queue returns input to the machine at once. A watchdog catches a half-open connection and retries it.

Crossing

Push the pointer at the outer edge and it does not move: the push builds as pressure, the edge lights up, the trackpad ticks at each quarter, and once you have pushed far enough the boundary gives. The resistance is the point. An edge that switches the instant you touch it does so every time you overshoot a close button. The default is 120 points; zero switches on contact.

Way in	Where it triggers	Mac	Windows
Shortcut	Double-tap the trigger key, or hold it	Yes	Yes
Edge	The whole of one outer edge	Yes	Yes
Part of the edge	Only the thirds of that edge you pick (start, middle, end), measured on the display under the pointer	Yes	Yes
Corner	An 8pt box in one corner, needing a diagonal push	Yes	Yes
Notch	The top edge, only within the notch's width	Yes	No

Any combination can be on, except Edge and Part of the edge, which exclude each other. On the Mac, Shortcut and the right-hand edge are on to start with. On Linux under Wayland, the shortcut only brings input back; the desktop only lets it go to another machine at an edge.

• The notch has no pixels to light, so a push there draws on the notch itself. Outline, the default, runs a comet of light round a small tab under the notch that brightens and speeds up with the push. Island springs a black island out of the notch with a four-segment meter; with Reduce Motion on it stays one size and fades with the push.
• An edge counts wherever no display of the same machine lies beyond it, so an edge between two displays behaves as the system intends, and the edge of a MacBook under a wider external display still crosses.
• The pointer arrives where it left: 42% of the way down the Mac's right edge is 42% of the way down the PC's left edge, on whichever monitor owns it.
• On macOS and Windows, crossing does not fire while a mouse button is held, so a drag that reaches the edge stays a drag. On Wayland, the desktop can capture a drag at the edge.
• The full-screen hold is off by default. When enabled on macOS or Windows, a full-screen app on that screen holds pointer crossings; it does not apply to Beamer's own window. Shortcuts and jump keys still work. Wayland cannot detect a full-screen app.
• Only one machine's input is on another at a time. The receiving machine can send it home or pass it on through one of its own configured zones.
• A machine's own switch, menu or shortcut sends input home. On Wayland, the shortcut only brings input back.
• Switching to a sleeping PC sends wake-on-LAN when that PC supports it.

Each machine's menu lists its peers and the directions it can drive. Turning one direction off leaves the other direction alone.

Keys, buttons and media keys

For a Mac-to-Windows pair, Mac modifiers map to Windows by meaning, so the shortcuts your fingers know keep working. The Mac's Keyboard page can switch this to positional, where Cmd sends the Windows key. Mac-to-Mac and Windows-to-Windows pairs keep each physical key in place.

Mac key	Sends on Windows
Cmd	Ctrl
Ctrl	Windows key
Option	Alt

So Cmd+C, Cmd+V, Cmd+Z and Cmd+T are copy, paste, undo and new tab, Ctrl+E opens Explorer and Ctrl on its own opens Start. The PC's keys arrive on the Mac the reverse way. Chords with Ctrl, Alt or Windows held are sent as real virtual-key presses, so they land on the right key for the active Windows keyboard layout. The Mac reads its own layout too, so on a German or French Mac Cmd+Z is still undo and Cmd+A still selects all, and a letter typed from the PC lands on the key that types it. When the two machines are on layouts of different alphabets, say the PC on Russian and the Mac on English, a letter types what the receiving machine's own layout has on that key, as its own keyboard would, and shortcuts keep working. The key_map object in each app's config JSON can still override single keys.

The trigger key is never forwarded on macOS and Windows. It is recorded by pressing it: Right Option on the Mac and Right Ctrl on Windows to start with. Either can double-tap or hold.

The stays-here list is per machine, because a Mac keycode and a Windows virtual key are different numbers for the same key. It takes keys, the right, middle, back and forward mouse buttons, and on the Mac its media keys. A listed press stays on the machine it was pressed on while input is away; its release goes wherever its press went, so nothing is ever left held down on the far side. The trigger key cannot be added.

The Mac's F7–F12 media row and volume keys cross as play/pause, next, previous, mute and volume. On the Mac they arrive as system events rather than key events and are captured separately (mac_app/media_keys.py). Brightness and keyboard-backlight keys stay with macOS.

Ctrl+Alt+Del is the Secure Attention Sequence, trapped by the kernel before any app sees it. SendInput cannot produce it, and SendSAS() needs a Windows service or a signed uiAccess app installed under Program Files, which Beamer is not.

Gestures

Trackpad scrolling is smooth and horizontal scrolling works on Windows. While input is on Windows, the Mac's system gestures do the equivalent thing there and nothing on the Mac:

Mac gesture	On Windows
Three or four fingers up (Mission Control)	Task View
Three or four fingers down (App Exposé)	Show desktop
Three or four fingers left or right (Spaces)	Switch virtual desktop, the same way round
Thumb and three fingers spread (Show desktop)	Show desktop
Thumb and three fingers pinched (Launchpad)	Start

A two-finger pinch and a two-finger swipe between pages are not passed to the other machine yet.

The Mac classifies a system gesture when it ends and sends one message. The PC replays it as a real swipe through a synthetic Precision Touchpad, so Windows' own touchpad settings apply and Task View animates as it would under fingers. Where Windows refuses that device, it presses the shortcut with the same default meaning instead (Win+Tab, Win+D, Win+Ctrl+Left/Right, Win). Direction comes from private macOS event fields, keyed by macOS major version in mac_app/gestures.py, because the horizontal sign has flipped between releases.

Clipboard

The clipboard moves at the moment of a switch, ahead of the switch itself: switching to another machine carries the current machine's clipboard, and switching back carries the other machine's. Where it holds both an image and text, both cross and the pasting app picks. The caps keep the switch prompt: 256KB of text and an 8MB image as PNG. Over a cap, that half is left alone rather than truncated. The PC converts to and from the Windows clipboard's DIB format itself, using the Qt it already ships. A switch sends the clipboard only when it has changed since it last crossed, so a large image is not re-sent every time.

Latency

If both machines are on Wi-Fi, every event crosses the air twice, through the access point. Ethernet on either machine removes a hop. Where Wi-Fi is unavoidable, 5GHz or 6GHz and turning off power saving on the PC's adapter both help.

Beamer sends every event at once (TCP_NODELAY). Acknowledgements are coalesced over 15ms so a 100Hz stream of moves cannot double the packet count, with an idle heartbeat every 400ms. Settings show the measured round trip while input is on another machine.

Security

Wire version 6 combines each paired token with a fresh X25519 exchange to derive directional keys with HKDF-SHA256. Frames are sealed with ChaCha20-Poly1305. Pairing agrees a token with CPace, a password-authenticated key exchange, from the six-digit code. What that does and does not protect against is in SECURITY.md.

Update check

Once a day, and at start, Beamer asks GitHub's public releases API for the latest release of this repository and compares its version with its own. A new minor or major version is always offered; a patch release (1.5.0 to 1.5.1) only when its release notes ask for it, so a run of small fixes does not nag. Drafts and pre-releases never count and nothing is downloaded. When a newer one is out, the menu says Beamer X is available and Overview offers a Download button that opens the release page. The request is an ordinary HTTPS request, so GitHub sees the address it came from, as it would for a browser. Switch it off with Check for updates on Overview.

Windows specifics

The installer puts Beamer in %LOCALAPPDATA%\Beamer for the current user with a Start menu shortcut. Quit Beamer from the tray before installing a newer version over it; only one instance runs at a time.

Beamer runs elevated (its exe carries a requireAdministrator manifest), because Windows silently drops input from a non-elevated app aimed at an elevated window such as an admin PowerShell. Start Beamer when you sign in, on Overview, writes and removes an elevated Beamer logon task; nothing else touches autostart.

Beamer needs two inbound rules on Private networks: TCP 24820 for input and UDP 24821 for pairing, both below the range Windows and macOS hand out for themselves. The app adds them on its first elevated start. Connection says in one sentence whether the Mac can get in and offers one button for whichever of three things usually stops it: the rule is missing (it adds it), Cancel was pressed on Windows' own "allow this app" prompt, which writes a block rule that beats any allow rule (it removes the block and adds the rule), or the network is classed as public (it marks the network private rather than opening the port on every public network).

The lock screen. No elevation lets an app type there: it is the Winlogon secure desktop, which admits only SYSTEM. On a PC with the author's separate unlock credential provider installed (not part of this repository), switching to a locked PC signals that provider, which unlocks it in about four seconds; input sent meanwhile is dropped. Beamer only signals the provider and never holds a password. Without it, the Mac reports Windows is locked — unlock it at the PC.

Linux

Linux support is experimental. Install the x86_64 Flatpak from the release page with flatpak install --user Beamer-<version>-x86_64.flatpak, or build it with the Flatpak instructions. On one Fedora 44 GNOME desktop under Wayland, paired with a Mac and with a Windows PC, the window and tray, pairing, crossing both ways, typing and the clipboard work; there, crossings show no edge animation on the Linux machine and the selected option in settings is not filled in. X11 on real hardware has not been tested. Flatpak needs Flathub to install the KDE runtime if it is not already present. The same package is built for GNOME under Wayland and for X11.

On Wayland, the desktop limits what Beamer can do:

• “On Wayland the shortcut only brings input back: the desktop lets input go to another machine only when the pointer pushes through an edge, and keys on the Stays on this PC list cannot stay here while input is away.”
• “On Wayland Beamer cannot see a full-screen app, or a mouse button held before the pointer reaches an edge, so the edges are never held for one and a drag can cross.”
• “On Wayland the desktop does not let Beamer draw at the edges of the screen, so crossings show no effect on this machine. The other machines still show theirs.”

Linux does not offer gestures. KDE Plasma has not been tested.

Building from source

On the Mac, double-click mac_app/Install-Beamer-Mac.command. It builds a self-contained app, installs it at /Applications/Beamer.app, and leaves it closed so the permission prompts do not appear unexpectedly.

On Windows, run win_app\Install-Beamer.ps1 from an admin PowerShell. It builds and installs %LOCALAPPDATA%\Beamer\Beamer.exe, adds a Start menu shortcut and the two firewall rules. From a non-admin PowerShell it still installs but skips the rules, which the app adds on its first elevated start.

Pairing is the easy path, not the only one: each Connection page still takes an address, port and shared token typed by hand, and they must match on both machines.

Development checks

From mac_app:

.venv/bin/python3 -m unittest discover -s tests -v
./build_dmg.sh

From win_app:

python -m unittest discover -s tests -v
.\build_win_app.ps1

A local Mac build is signed with the release's Developer ID identity when the login keychain can reach it, so privacy grants carry between local builds and releases, and ad-hoc otherwise (over SSH), under the hardened runtime either way. It is not notarised.

What both apps run the same way (protocol.py, pairing.py, receiver.py, return_edge.py, the crossing effects and others) lives once in core/, which both apps import and both packagers bundle; core/tests runs inside each app's suite. Linux uses the Windows app's Qt shell and its Linux back ends, packaged as a Flatpak. tokens.py is still copied into win_app, and a test fails if the two drift. Beamer.svg is the master of the mark, and Beamer.ico, Beamer.png and Beamer.icns are rendered from it.

Release builds

The version lives once, in VERSION at the repository root; the Mac build number is the commit count. Change VERSION, commit, then build each platform from that commit. Both commands refuse uncommitted changes outside docs/, upload nothing except the Mac's notary submissions, and write to docs/beamer-releases/<version>/ in the folder that contains the repository.

On the Mac, from mac_app, in a desktop session (the keychain will not release a Developer ID identity over SSH):

./build_dmg.sh --release

It signs every nested binary with Developer ID under the hardened runtime with a secure timestamp, checks the bundle still runs, notarises and staples the app, then the DMG, and checks both with stapler validate and spctl. Notarisation uses the App Store Connect API key named in ~/.appstoreconnect/key_id.

On Windows, from win_app:

.\build_win_app.ps1 -Release

It runs the tests, builds Beamer.exe and compiles Beamer-Setup.iss with Inno Setup 6 into Beamer-Setup-<version>.exe. The installer adds no firewall rules and leaves autostart off.

Licence and support

GPL-3.0; see LICENSE. Releases up to and including 1.2.0 were MIT.

Beamer is free and made by one person. Issues are welcome and read, but there is no guarantee of a reply. Before a pull request, read CONTRIBUTING.md. Report security problems privately, as SECURITY.md describes. Home page: kalkmancode.co.uk/beamer.

A bug report is far easier to act on with each machine's log attached. Open log folder in each machine's menu opens it: ~/Library/Logs/Beamer/Beamer.log on the Mac and %LOCALAPPDATA%\Beamer\Beamer.log on Windows. They hold your machines' names and local network addresses, so look them over before posting.