Anything about Mahara software development, or developing for Mahara:
- Core development
- Developing new plugins
Note that the Mahara core developers tend to discuss things in #mahara-dev on freenode. You're welcome to lurk there, and listen in on conversations, but it's only for discussions about Mahara's development itself - you can use #mahara for those questions.
Also, check out the developer area of the wiki - it has information about Mahara's internals and on how to write plugins.