Design Principles - An open source repository of design principles and methods
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Facebook Design Resources - A collection of free resources made by designers at Facebook
Teampaper Snap - Take a snapshot, highlight key areas and share feedback
Facebook - Connect with friends, family and other people you know. Share photos and videos, send messages and get updates.
Inspect by InVision - A magical new design to development workflow from InVision