This plugin was a first attempt to bring version control and collaboration to designers. Since then, Sketch evolved a lot and my new project takes advantages of them to unlock true version control. Check it out: http://kactus.io
A Git client built right into Sketch. Generate pretty diffs so that everybody knows what are the changes!
Sketch >= 3.4 (not with the sandboxed version ie from the App Store).
Git (coming with OS X so you shouldn't have to do anything)