Project Babel is a software package for running a community on Google App Engine. It's written in Python and released under very liberal BSD license. You can use it, modify it or even sell it whatever way you want.
Features:
- Topics are organized under Nodes (Discussion Areas), you can have many Nodes in one community - Nodes can have header, foot and category property, or organized under Sections - Two clean themes: one for desktop browser, another for iOS device and Android - Optimized for modern browsers - Built-in WebDAV avatar facility, you can host all avatars with MobileMe or other WebDAV servers - Atom feed output - HTML5 - Built-in MapReduce tasks for optimizing community data - Built-in OAuth Twitter client for tweeting and syncing topics/replies - Built-in Notes feature