It sports 8 tracks with two possible instruments on each of them (16 different instruments max), looped on a 16 beats track.
It is controlled by a USB gamepad or a keyboard, and can be used live (ie changing patterns or editing them)
It works by playing and modifying patterns on a mod file on the SD card (samples can be bigger than the bitbox memory), so you can create drumkits quite easily with a Tracker and play/modify it on the bitbox.
Of course, it's free and open sourced ! See sources and graphics on GitHub