I recently developed an Android app which integrates with your OSSN site to allow users to engage in messaging from directly within the Android app. Users can message other users of the app, or members of your OSSN website - the messages will show up in both places. Additionally, it makes use of many components which I added including:

• add media (images/audio) to messages
• read receipts for messages
• forward messages
• user is typing notification

The above 4 additions work both on your OSSN site and the app. Below are some screenshots.

Select conversation screen showing new/unread messages:

Conversation between 2 users, showing audio file, read receipts, and user is typing notification:

Additionally, the app will show native Android system notifications for incoming messages when the app is not in the foreground (the standard type of notifications that android apps receive). An iOS version of the same will be available imminently. Please contact me if you are interested (email in profile).