Animation branches
There are actually two animation branch for MyPaint. Both use some tricks on layer to use them as frames.
 Charbelinho branch
- Charbelinho branch (march 2010)
 X-Sheet MyPaint branch
It was developed to make a short film, Viaje a la tierra del Quebracho. Currently, it's not ready to be widely usable, but there is a plan to do it in the future (read below).
It presents a widget that resembles an exposure sheet (x-sheet for shortness), an important tool in traditional animation. That way it's possible to plan your work marking frames as keyframes, adding inbetweens, animating on one's or on two's, and a lot more. It can save frames as a PNG sequence, and export to video if ffmpeg is available in the system.
Code tries to be as much separated as possible from MyPaint's mainline code, so it was easy to keep it in sync with latest MyPaint for a while, until manuq, the developer, was busy as the director of the short film mentioned above. In the future, it would be nice to make it an application in it's own using the brushlib.