Open Peeps - A hand-drawn illustration library.
Spine - Spine is 2D animation software designed specifically for software and game development.
Control Illustrations - 108 free flat illustrations with customizable characters
Synfig Studio - Just another WordPress site
Handsome Illustrations - Create unique illustrations for websites & applications.
AnimeEffects - AnimeEffects is a 2D keyframe animation tool based on deformation of polygon meshes.