Dotpict - Easy and intuitive, mobile pixel art editor.
OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Synfig Studio - Just another WordPress site
Spine - Spine is 2D animation software designed specifically for software and game development.
Adobe Animate - Adobe Animate is a Flash, vector animation software.