Callipeg is a 2d animation app for the iPad which offers professional animation tools adapted to iOS ergonomics and design. Everything is designed for the Apple Pencil and hand gestures, from the ...

Pencil is a very realistic sketching program and good 2D animation tool for the cost (free).

The Grease Pencil provides 2d animation tools within Blender's free and open-source full-3d pipeline.