It started was mac only, but with 2.5 its now available to windows users as well. Unfortunately you have to pay for this(30 day trial though), but the indie package costs 200$, the full package costs 1500$. absolutely not a bad price considering the potential we got here.
Blurst got some crazy games made with it, good examples
Blog about the fancyness of unity 3d.
Personally i've been looking around for something like this. If i find the time for it in the near future I'd love to create something fancy with these tools.
another edit: found a list of the differences between the indie and pro versions. link
Edited by duke_Qa, 29 March 2009 - 02:56 PM.