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!
Open Peeps - A hand-drawn illustration library.
Validately - Validately is a user feedback platform to test demand and usability on a clickable prototype or live feature.
Control Illustrations - 108 free flat illustrations with customizable characters
UserZoom - Test, measure, and monitor UX with our cost-effective all-in-one platform. UserZoom is a cloud-based solution for online usability testing.
DrawKit - MIT licensed SVG illustrations, in 2 styles