But this is just a plug in for the IAR workbench or the Keil MDK and although the plug in might be free the things it plugs into are not as I understand it. I couldn't see any reference to multi platform so I assume it can't be run on a Mac easily.
Finally while it is a development system it is not as easy as the aduino for making stand alone gadgets from the processor and a few bits. Supporting only surface mount devices also makes it necessary to make a PCB before prototyping.
So while it is interesting if you need the grunt I don't think it is an ardunio killer.