SketchTool - Export pages & slices out of .sketch docs using CLI
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Select Similar Layers - Sketch plugin to select layers with the same attributes
InVision Studio - The world’s most powerful screen design tool
Base UI Sketch Framework - Huge set of everything you need to design and prototype
Design Principles - An open source repository of design principles and methods