OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
Spine - Spine is 2D animation software designed specifically for software and game development.
Synfig Studio - Just another WordPress site
Creature - Creature 2D Skeletal and Mesh Animation Tool
Adobe Animate - Adobe Animate is a Flash, vector animation software.
Unity 2D - Unity 2D is a powerful and feature-rich game design solution built from the ground up to fulfill every basic and advanced need of the developer.