Git Sketch Plugin - Version control for designers
Brand.ai - Create a style guide & integrate with Sketch, Slack, & Gulp
Anima App - Design, get feedback, convert to code, publish, iterate.
Sketch Styler - Sets the most similar style to unstyled layers automatically
Marvel for Sketch - Sync, play and record prototypes in Sketch!
Sketch Repo - Collection of resources for anyone who uses Sketch