Anima App - Design, get feedback, convert to code, publish, iterate.
Fluid for Sketch - Sketch plugin to make your responsive designs more efficient
Sketch Repo - Collection of resources for anyone who uses Sketch
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Auto-Layout for Sketch - Responsive design for Sketch
Overframe - Record your prototype & app with device frame overlay.