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.

The Arduino Team presented some new products at Maker Faire this weekend. It’s a significant update. The Arduino UNO and Arduino Mega 2560 update the Duemilanove and Mega respectively. They n… ...

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.

Chuck Todd has built a Arduino compatible Mega2560 expansion RAM that will enable those using the Arduino platform who need more that 8k RAM in the Arduino processor.