We've provided the following documentation specifically for developers:
- libjingle: an open-source C++ library that you can use to build peer-to-peer applications for voice, video, or file-sharing. The code handles both connection negotiation and data exchange.
- Google Talk XMPP extensions: describes the non-standard XMPP extensions used by the Google Talk server. If you build an XMPP client, you can listen for and use these extensions to provide greater functionality to your application.
- Google Talk and Open Communications: answers some basic questions about the protocol and codecs used by Google Talk, as well as future goals and federation.