500

An Android and web app for 500, the classic 4-player partnership trick-taking card game (Australian rules). Play offline against AI opponents, or online with friends — cross-play between Android and the browser, with bots filling any empty seats. Play it now in your browser: https://rotundtapir.github.io/500/

Built on the shared cardkit library (included here as a git submodule), the first of a suite of card-game apps. Where it's heading: ROADMAP.md.

Distribution

Channel	Ads	Support
Google Play	Banner + occasional interstitial (Google Mobile Ads), with a one-time in-app purchase to remove them	purchase
F-Droid / GitHub releases	None — no ads, no trackers, no proprietary code	donation link

The two are the play and foss build flavors. The F-Droid build excludes the cardkit-monetization-play module entirely, so it contains no non-free code.

Install / play

• Web: play instantly at https://rotundtapir.github.io/500/ — no install.
• GitHub: signed ad-free APKs are attached to releases (install directly; updates keep the same signature).
• Google Play: in closed testing (ad-supported flavor) — testers wanted, see below.
• F-Droid:

Support development via Liberapay.

Help get 500 onto Google Play

Google only lets a new app into production after at least 12 people have been opted in to a closed test for 14 days. The game is finished and already on F-Droid and the web; this is purely the paperwork, and you can help in two minutes:

1. Send the Google account email you use on your phone to rotund_tapir@protonmail.com with the subject "500 beta" (it is only used to add you to the tester list; you can ask to be removed any time).
2. Once added, open https://play.google.com/apps/testing/io.github.rotundtapir.fivehundred on that account, accept, and install from Play.
3. Keep it installed for two weeks. Playing is welcome but not required.

Bugs and suggestions go to the issue tracker.

One signature everywhere

The foss release build is reproducible: a clean checkout of a release tag rebuilds the GitHub-release APK bit-for-bit (only the signing block differs). The F-Droid listing uses this so F-Droid can verify its own rebuild against our release asset and publish the developer-signed APK — the same file as on GitHub releases, so you can switch install sources without uninstalling. The release signing certificate's SHA-256 fingerprint is:

86c486105ed5062b90815fec97311029ab5569735926c323c7896c8d64b78d65

Building

git clone --recurse-submodules <repo-url>
cd 500
./gradlew :engine:jvmTest       # run the rules engine unit tests (JDK 21, no Android SDK needed)
./gradlew :server:test          # online server tests (JVM; real-WebSocket integration)
./gradlew assembleFossDebug     # ad-free debug APK
./gradlew assemblePlayDebug     # ad-supported debug APK
./gradlew :web:wasmJsBrowserRun # run the web build locally (http://localhost:8080)

Requires JDK 21 and, for the app modules, the Android SDK (compileSdk 36).

Project layout

500/
├── cardkit/     # shared library (git submodule), wired in via includeBuild
├── engine/      # pure-Kotlin 500 rules: deck, bidding, tricks, scoring
├── ai/          # heuristic bot strategy
├── net/         # online wire protocol + client (KMP jvm+wasmJs)
├── server/      # authoritative online server (JVM Ktor); Docker/deploy in server/deploy
├── shared/      # Compose Multiplatform game UI (offline + online), android+wasmJs
├── app/         # Android shell; foss/play flavors
└── web/         # browser (Kotlin/Wasm) shell

The rules engine is pure Kotlin with no Android dependency, so it is fully unit-tested and runs server-side — which is exactly what the online server does, driving the same engine one game room at a time.

The game

Standard 4-player Australian 500: a 43-card deck (4→A in hearts & diamonds, 5→A in spades & clubs, plus one Joker), 10 cards each and a 3-card kitty; bidding from 6 to 10 tricks across the suits and no-trumps, plus Misère and Open Misère; first partnership to 500 points wins.

License

GPLv3-or-later with a Google Mobile Ads / Play Billing linking exception — see LICENSE and LICENSE-EXCEPTION.md. Contributions require a DCO sign-off; see CONTRIBUTING.md.

Namespace: io.github.rotundtapir.* (and the applicationId io.github.rotundtapir.fivehundred) is the io.github.<account> namespace of the GitHub account rotundtapir that publishes this app.