The idea early on was to leverage existing Arduino libraries to connect with a standard USB mouse, specifically, the hardware would take the form of an Arduino Mega 2560 with a USB Host Shield.

If you are searching for a new project to keep you busy for the next couple of weekends you might be interested in this hexapod robot project powered by an Arduino Mega 2560 development board ...

It's of course backwards compatible with existing Arduino add-ons, but sets itself apart with a new USB controller with lower latency and driver-free operation on Mac and Linux.