Synfig Studio is a free and open-source 2D animation software, designed as powerful industrial-strength solution for creating film-quality animation using a vector and bitmap artwork. It eliminates the need to create animation frame-by frame, allowing you to produce 2D animation of a higher quality with fewer people and resources.
Can manipulate vector and bitmap artwork
Automatic tweening (independent from FPS)
Multitude of layers of various types (geometry primitives, shapes, gradients, fractals)
Full-featured bone system
Filters and effects for compositing (blurs, distortions, color manipulation, masks)
All color operations use High Dynamic-Range Imaging (HDRI)