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!

Axure - The most powerful way to plan, prototype and hand off to developers, all without code. Download a free trial and see why professionals choose Axure RP 9.

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

Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.

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

Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project