The Sketch component of the Craft prototyping tool works pretty good — still a bit barebones, but works. The problem I have with it, is with the viewing of the prototype either on the web or in the InVision native mobile app. Syncing keeps pulling in unselected and unlinked artboards and missing the ones that are, or is missing the links I’ve set up between dartboards. And the omnipresent black status bar is annoying and not configurable. This isn’t ready for prime time in my opinion. If you can’t view the prototype properly, then it’s not much of a prototyping tool.