UserTesting.com - Usability testing has never been easier. Get videos of real people speaking their thoughts as they use websites, mobile apps, prototypes and more!

TrackIR - TrackIR adds depth to the PC gaming experience by enabling players to take control of the in-game view.

Userbrain - Easy, fast, and affordable user testing for websites and prototypes.

linux-track - Linuxtrack is a software bringing headtracking to Linux and Mac OS X.

userinput.io - Get on-demand feedback for your app, website or idea. Learn how to improve by hearing real opinions.

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