One Click Test - Tool for quickly testing your design layout in one click.
Anima App - Design, get feedback, convert to code, publish, iterate.
W3C Mobile Checker - Make websites work better on mobile devices
Fluid for Sketch - Sketch plugin to make your responsive designs more efficient
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.
Git Sketch Plugin - Version control for designers