This covers the open source application blender (BlenderWiki).
The major portion of development discussion is at:
http://www.blender.org/mailman/listinfo/bf-committers
Another place to go is the tuhopuu "evil tree" discussion list:
http://www.blender.org/mailman/listinfo/tuhopuu-dev
Tuhopuu is mostly a prooving ground for new features.
Try
http://www.blender.org/mailman/listinfo/
for other aspects of blender development, or try
The blender source follows a general sort of naming convention: the directory 'intern' is module-level stuff, 'extern' is for the API files. Some of the times 'extern' is missing and the API is defined in the root directory.
eg:
The blender source is broken into several directories:
Intern is where a lot of the (mostly) independent modules are, such as GHOST, memory managment routines, the sound system, ik, etc. WARNING: the python in this directory is not where the current development is taking place!
Source is where the main action takes place. The 'creator' directory is where the main() function lives. The 'blender' directory is where the majority of the GUI, python, mesh stuff, etc lives. Not sure what the other directories are used for, beyond the obvious.
Okay, that's the basic directory structure layout. Now for the source layout. This part of the discussion will focus on the 'blender/source/blender' directory.
This is the extent of my knowledge. I will be adding more as time permits