I came across Pi-Supply’s Pi-Crust add-on board quite by chance, but it immediately caught my eye as quite possibly the most useful add-on for the Raspberry Pi there is. Having ordered one, received it and soldered all the parts together, I’m no longer sure that it is.
The notion behind the device is very sound indeed. It’s an internal breakout board that doesn’t merely replicate the Pi’s GPIO ports, it re-organises and labels them logically and clearly. It’s also intended to fit snuggly within the form-factor of the Pi itself. This is, frankly, a brilliant idea.