Git Sketch Plugin - Version control for designers
Fabricator - Build your UI toolkit for website design
Fluid for Sketch - Sketch plugin to make your responsive designs more efficient
Subform - A CAD-inspired design tool for UX/UI design.
Sketch Plugin Course by Design+Code - Enhance your design workflow by creating a Sketch plugin
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.