Visily - The easiest and most powerful wireframe software for agile teams.
SketchTool - Export pages & slices out of .sketch docs using CLI
PSD to Sketch Design Converter - Convert a Photoshop design to a layered Sketch file for free
Select Similar Layers - Sketch plugin to select layers with the same attributes
Zeplin - Collaboration app for UI designers & frontend developers
Base UI Sketch Framework - Huge set of everything you need to design and prototype