I just stumbled upon a free and open source animation app today. It is called OpenToonz, and is based on the Toonz animation software used by animation giant Studio Ghibli!

I apologize for the sudden disappearance of your free time.

Link to the software page (downloads and forums):

https://opentoonz.github.io/e/

Link to some nice tutorials on YouTube (since the PDF manual is only available in Japanese...):

https://www.youtube.com/playlist?lis...94GL-kJ41KMZOb