Your boy Jeremy Bullock has been contributing to OpenToonz, and him and many other contributors have came out with a new version of OTX (experimental openToonz). It has a bunch of cool features!
https://www.youtube.com/watch?v=aeYZg8p6FG8&feature=youtu.be
I like to use OpenToonz for a bunch of Pixel art stuff myself, and something else pretty soon yooo.