Minimus is an AT90USB162 based USB Key. It has an AVR with hardware USB, a DFU bootloader, 2 LEDs and a Button. A number of them were bought by uk hackspace members in February 2012.
Minimus as an AVR
It is supported by the LUFA (Lightweight USB Framework for AVR) Software Stack, Which is C based, and supported by GCC-AVR.
Programming the minimus is done through the use of Atmel FUSE (in windows) or using dfu-programmer Under osx and linux.
Bob has prepared the following cheat sheet, showing the pinout of all the minimus' extra features
In addition, Alan has some code that hooks the Minimus USART into ARR-libc so you can use the USART for debug statements etc, and it also provides a 1 millisecond clock tick. See the ABAVR project on SourceForge.
Minimus as an Arduino