C2K — Couch to 5K & 10K

Free, open-source running trainer for Android. No Google services. No tracking. No ads.

Features

• C25K — 9-week program to run 5K
• C210K — 14-week program to run 10K
• Bridge to 10K — 6-week bridge for C25K graduates
• One Hour Runner — 13-week progression to 60 minutes continuous running
• 5K Improver — 8-week speed and stamina program for runners who can already complete 5K
• Audible voice prompts (Android built-in TTS — no internet needed)
• Voice volume and speed controls
• Music ducking during voice announcements
• Background timer with lock-screen notification and pause/stop controls
• Optional GPS tracking (distance & pace) — works without it too
• Progress tracking across sessions
• Guide screen with FAQ and glossary
• Localised in English, Spanish, and Galician
• Fully offline — no internet permission
• Compatible with GrapheneOS and any de-Googled Android device (no Google Play Services)

Building

Requirements

• JDK 21 (install via SDKMAN: sdk install java 21.0.5-tem)
• Android SDK with platform API 36 and build-tools 36+ (install via Android Studio or sdkmanager)

Clone and build (debug)

git clone https://github.com/AnalogGhost/c2k.git
cd c2k
echo "sdk.dir=$HOME/Android/Sdk" > local.properties
./gradlew assembleFossDebug

APK: app/build/outputs/apk/foss/debug/app-foss-debug.apk

Run unit tests

./gradlew test

Install on device via ADB

adb install app/build/outputs/apk/foss/debug/app-foss-debug.apk

Release builds

Reproducible build (for F-Droid submission)

Use the Docker build script to produce an unsigned APK in the same environment F-Droid uses:

bash docker-build.sh

APK: app/build/outputs/apk/foss/release/app-foss-release-unsigned.apk

F-Droid builds from source and applies their own signature. Build from the tagged commit before making any further commits.

Signed (for personal sideloading)

1. Generate a keystore (one-time):

keytool -genkeypair -v \
  -keystore ~/c2k-release.jks \
  -alias c2k \
  -keyalg RSA -keysize 4096 \
  -validity 10000

2. Add to local.properties (this file is gitignored — never commit it):

sdk.dir=/home/YOUR_USER/Android/Sdk
storeFile=/home/YOUR_USER/c2k-release.jks
storePassword=YOUR_STORE_PASS
keyAlias=c2k
keyPassword=YOUR_KEY_PASS

3. Build and sign:

bash docker-build.sh

$HOME/Android/Sdk/build-tools/<version>/apksigner sign \
  --ks ~/c2k-release.jks \
  --ks-key-alias c2k \
  --ks-pass pass:YOUR_STORE_PASS \
  --key-pass pass:YOUR_KEY_PASS \
  --out app/build/outputs/apk/foss/release/app-foss-release-signed.apk \
  app/build/outputs/apk/foss/release/app-foss-release-unsigned.apk

F-Droid

C2K is available on F-Droid. The app metadata file is com.hackerapps.c2k.yml.

To release a new version:

1. Bump versionCode and versionName in app/build.gradle.kts
2. Add a changelog at fastlane/metadata/android/en-US/changelogs/<versionCode>.txt
3. Commit, tag, and push — F-Droid picks up new tags automatically:

git tag v1.x.x
git push origin main v1.x.x

See FDROID_PUBLISHING.md for the full initial submission guide.

Permissions explained

Permission	Why
FOREGROUND_SERVICE	Keeps the timer running with screen off
FOREGROUND_SERVICE_HEALTH	Required service type on Android 14+
WAKE_LOCK	Prevents CPU sleep mid-workout
POST_NOTIFICATIONS	Shows workout notification with pause/stop controls
ACCESS_FINE_LOCATION	Optional GPS for distance & pace — you can skip this
ACCESS_COARSE_LOCATION	Coarse fallback for location permission dialog

No INTERNET permission — the app is fully offline.

Project structure

app/src/main/kotlin/com/hackerapps/c2k/
├── data/
│   ├── model/        # Program definitions, interval types, coaching tips
│   ├── db/           # Room database — sessions and GPS route points
│   ├── repository/   # SessionRepository
│   └── prefs/        # DataStore user preferences
├── engine/
│   ├── WorkoutEngine.kt   # Coroutine tick loop, state machine
│   ├── WorkoutState.kt    # Sealed class: Idle / Active / Paused / Completed
│   └── tts/               # TextToSpeech wrapper, audio focus, announcements
├── service/
│   └── WorkoutService.kt  # ForegroundService, wake lock, notification
├── location/              # GPS abstraction (graceful fallback if unavailable)
└── ui/
    ├── screen/home/         # Program selection, recent history, streak
    ├── screen/program/      # Week/day picker with completion badges
    ├── screen/workout/      # Live timer, interval ring, distance/pace
    ├── screen/history/      # Past sessions list with CSV/GPX export
    ├── screen/settings/     # Voice, GPS, vibration, display preferences
    ├── screen/guide/        # FAQ and glossary
    └── screen/contributors/ # Contributors credits

Contributing

See CONTRIBUTING.md for how to contribute, including translation credits.

License

Copyright (C) 2026 Contributors

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

See LICENSE for the full text.