Spine - Spine is 2D animation software designed specifically for software and game development.
TrackIR - TrackIR adds depth to the PC gaming experience by enabling players to take control of the in-game view.
Synfig Studio - Just another WordPress site
linux-track - Linuxtrack is a software bringing headtracking to Linux and Mac OS X.
DragonBones - DragonBones is an open source project for 2D skeletal animation.
VSeeFace - VSeeFace is a free, highly configurable face and hand tracking VRM and VSFAvatar avatar puppeteering program for virtual youtubers with a focus on robust tracking and high image quality