TVPaint Developpement

Easy to learn and even easier to use. I've used it for every single stage of the animation pipeline: preproduction (animatics with easy to edit audio options!), production (the built-in camera makes it painless to plan my shots inside the program without having to depend on AE), and post-production (shading, textures or color correction can all be done IN the shot, no need to export to an outside program).