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!

UserTest.io - User testing made simple. High-quality, affordable user testing solutions from real users, here in the UK. Improve your usability!

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

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

UXtweak - Online user testing and usability platform

Validately - Validately is a user feedback platform to test demand and usability on a clickable prototype or live feature.