Zeplin - Collaboration app for UI designers & frontend developers
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Handoff by Marvel - Automatically turn designs into assets, specs and code
Facebook Design - Resources for Designers from the Facebook Design team
InVision Studio - The world’s most powerful screen design tool
Handoff Helpers - Free Figma library to make designers better communicators