Krita, an actual FREE digital art program, recently released an Alpha 3.0 version that features tools for creating “hand-drawn animations”.
If you’re looking for an art program with more advanced tools than Paint Tool Sai but don’t want to cough up the cash, then Krita is your program. (However donations to support the people making the program are very much appreciated!)
I understand that when you first download it, the layout and tools can be a little intimidating, but don’t worry. The program comes with a manual and there are tutorials on Youtube that can help you understand the basics.
Even if you don’t want to download this program or donate, please reblog to help spread the word and tag people you think might enjoy this.
Edit: Also, there are different brush packs you can download here. And if you don’t like this program there is also MediBang Paint.