Dnotes (download source) is a basic animation program. It runs on both Linux and Windows (and very probably MacOS too). It requires Python (2.*) and Pygame to run.
There is a modified linux version (download source) that is also able to export the animation to mp4 using ffmpeg. It will work on windows, except that it will crash if you try to export the animation.
python dnotes.py [FILE]
* will launch dnotes on FILE (creates it if non existent) python dnotes_2_mp4.py FILE
* will launch dnotes on FILE (don’t pay attention to the program name: this is just the same as dnotes.py with 2 additional functions)
Currently there is no eraser in the Web version, and a lot of other options are missing, but the basic tools are there (and onion skin too).