and in current release F# (current being pre-Build 2.0, i.e. RTM for over a year, tho I can't comment on whether you'd really like to have VS Ultimate to make it work)
The current release is included in VS Professional, Ultimate isn't required. It seems like the last recent installer for VS Shell is the CTP, so expect some difficulties if you want to go the free route on windows, although it's possible that SharpDevelop integrates with the latest source drop.
Anyway, it shouldn't be too difficult to build the compiler yourself and set up a basic emacs/vim + mono environment for linux.
