PSD to Sketch Design Converter - Convert a Photoshop design to a layered Sketch file for free
Zeplin - Collaboration app for UI designers & frontend developers
avocode - Centralize design collaboration, version control, prototyping, feedback, and developer hand-off with Avocode. Work on any design, anywhere, with anyone. Sign up free 👉 https://avocode.com/.
Sketch Repo - Collection of resources for anyone who uses Sketch
Sympli - Design handoff & collaboration for Figma, Adobe XD, Sketch, and Adobe Photoshop. Design Verison control for Sketch.
Auto-Layout for Sketch - Responsive design for Sketch