krita can be used to create flip books.

http://danielcwilson.com/blog/2015/07/animations-intro/ and http://rachelnabors.com/alice-in-videoland/book/ via http://shoptalkshow.com/episodes/203-with-rachel-nabors-and-dan-wilson/

http://rachelnabors.com/waapi via http://thewebplatformpodcast.com/141-web-animations-api