Maze - Beautiful & actionable analytics for InVision prototypes
ProtoPie - ProtoPie is the easiest tool used to turn your UI/UX design ideas into highly interactive prototypes for mobile, desktop, web, all the way to IoT.
Conversion Crimes - Get insights on how users behave on your site or software and how they feel about it. Remove friction and increase motivation to buy.
W3C Mobile Checker - Make websites work better on mobile devices
Koncept - Usability testing, interactive prototypes & metrics
Dimensions Toolkit - Chrome Extension for designers to test responsive websites.