Sketch 42 - Now with export presets, touch bar integration, and more
Now UI Kit - A beautiful Bootstrap 4 UI kit. Yours free.
Anima App - Design, get feedback, convert to code, publish, iterate.
Invision - Prototyping and collaboration for design teams
Sketch Repo - Collection of resources for anyone who uses Sketch
Avataaars - Mix and match avatars with a Sketch library