signal-cli provides an unofficial commandline, JSON-RPC and dbus interface for the Signal messenger.

OpenKeychain is an OpenPGP implementation for Android.

Better modification of the official Mastodon for Android app

Virtual Tabletop for playing roleplaying games with remote players or face to face.

configurable OSM offline router with elevation awareness, Java + Android

VASSAL, the open-source boardgame engine

Android Input Method Editor (IME) based on RTranslators Whisper implementation

Simple to use OpenPGP API based on Bouncy Castle