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
Fluid for Sketch - Sketch plugin to make your responsive designs more efficient
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.