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!
POP (Prototyping on Paper) - POP helps you make interactive prototype with ease. If you can draw, you can design apps.
Hotjar - The #1 Leader in Heatmaps, Recordings, Surveys & More. Sign up for a 15-day free trial and start learning from real user behavior today!
Briefs - Briefs is the essential app design tool built for a professional design workflow.
Balsamiq Mockups - Using Balsamiq Mockups feels like you are drawing, but its digital, so you can tweak and rearrange...
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.