I'll check it out, thanks for sharing! Looks promising from one one minute scan.

In a similar vein (also have zero affiliation) I discovered https://whimsical.com today, which also has a few other promising looking tools like flow diagrams, post-its etc.

Marvel App is a nice one. Sketch, photograph, wire photos together into a workflow mockup.

App Cooker on iPad is really nice too, though no longer maintained. It exports the storyboard of all the UI screens connected by transition arrows.