X Duino project extends the hardware horizon of Arduino which (as of today) is solely based on ATMEGA processor. The possibilities are are limitless.
Currently the following processor platforms are supported:
ARM Cortex-M3 of STM32F10x
(This list will keep expanding based on your contribution or if I can get a hold of more boards : -)
Currently no IDE is provided which means that users will need to obtain their own compiler (Arm GCC, Keil RV-MDK, IAR, etc) for this to work.
Development of Xduino IDE is under consideration.