Backed this a Kickstarter but haven't used it. It connects to the Chaos Audio app via Bluetooth, from which you can upload various effects to it, controlling the effect parameters from the app and the volume from the pedal itself. Essentially it can be any one of most types of pedal in your chain, fuzz, drive, compression, modulation, delay, reverb etc. The effects in the app are mostly a one-time payment (usually listed about $15 (£11.50), though they do have some free ones as well. Quite hard to price as there aren't many around, but it retails at $299 (£225) so I based a second hand price for an unused one on that.
eBay