Sketch Repo - Collection of resources for anyone who uses Sketch
Visily - The easiest and most powerful wireframe software for agile teams.
Zeplin - Collaboration app for UI designers & frontend developers
PSD to Sketch Design Converter - Convert a Photoshop design to a layered Sketch file for free
Auto-Layout for Sketch - Responsive design for Sketch
Anima App - Design, get feedback, convert to code, publish, iterate.