Besides being a chat client XtreMePP is designed for integration with other apps like LedEffects. Incoming messages are broadcasted so that other apps can react on incoming messages, in future version the accent will be put on messages as commands to interact with android apps using Intents. XtreMePP is an open client and of course is open source (http://www.cri.ch/sven/doku.php/computing/android/xtremepp).
Great app, would highly recommend it!