(Also goes by the name 'wine' under linux, but I figured more of us who don't use windows would likely be using the mac rather than linux)
Darwine, a project for intel macs based on wine, seeks to provide an API completely compatible with the windows API including DirectX. It's mainly used to play Windows games under unsupported operating systesms by those who do use it. I've ben fiddling around with the 1.0 release candidate under OS X Leopard, and after much registration of DLLs and other obscure files, I've finally gotten an audiogame working 100% under Mac OS X -- the game in question is Super Deekout. It's a little laggy, and the coins sound aliased and weird, but it is playable. I think some of the lag is due to my not being able to run the graphical configuration problem without sighted assistance (I'd've gotten some, but I don't have a monitor handy).
I've tried running other programs on it; NVDA (free windows screenreader) spoke for a split second before crashing with some obscure error, and the JFW installer worked before JAWS called a dozen unimplemented functions regarding the keyboard or something. I'm disappointed that I couldn't get NVDA working, because it would really make agreeing to licenses during installation of games a lot easier, and would mean I don't have to install a game on my windows machine so that I can copy it over and hope that all the needed components are available and registered. I might ask the NVDA developers about Wine compatability; it would be awesome to have a free desktop system like Linux with Gnome with the ability to run several common windows apps (wine can run office successfully from what I read) legally and for free.
I doubt many others will have feedback or interest in this, as I think most of us are almost-exclusive windows users, but I figured I'd give it a shot. Plus I'm extatic after finally getting something working.
Postscript: after rereading it I apparently wrote "wine configuration problem" rather than "wine configuration program." Haha how appropriate. Damn thing.