Git Sketch Plugin - Version control for designers
Anima App - Design, get feedback, convert to code, publish, iterate.
Sketch Repo - Collection of resources for anyone who uses Sketch
Marvel for Sketch - Sync, play and record prototypes in Sketch!
Marvel Sketch Plugin - Rapid mobile and web prototyping with Sketch
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.