With it, you can snap a photo with your phone, and immediately vectorize it for use in print, laser cutting, or desktop paper cutting. I always thought this should exist as a web service, since it can be a pain to open up Inkscape sometimes, and this is supposed to be a pretty well-solved problem.
It works on Android, fastest in Chrome – and only on Safari on iOS, probably due to Apple’s closed-browser strategy.
Here’s a snap of the output from the above image, opened in Inkscape to show the vector lines:
András’ library does a fantastic job; all I did was connect it to a file upload form and ensure the SVG downloads well, and make a nice interface with a settings dialog. This last could be expanded, as well.