I guess people working in 2D animation are well aware of this, but it seems to be a big deal:
http://www.cartoonbrew.com/tech/toonz-s ... 38111.html
http://www.cartoonbrew.com/tech/heres-d ... 38465.html
https://opentoonz.github.io/e/index.html
https://github.com/opentoonz/opentoonz
Sadly only for Windows and Macs so far.