x262 is an MPEG-2 encoder based on the best-in-class features of x264.
It also has the big advantage that the codec is simple enough for people new to video-compression to get involved.
The TODO list can be found here.
The latest x264 source code can always be found by anonymous git repository:
# git clone http://git.videolan.org/git/x262.git
You can browse the source on-line.
For support information and to ask questions, you have the following possibilities:
x262 is licensed under the GNU GPL.