Its the program that means I don't have to use iTunes.
+++
To give you a "real" answer, King...
Parallels Desktop (and
VMWare's Fusion) are programs for MacOSX that allow you to run a "virtual" copy of Windows inside of OSX, which allows you to run Windows-only applications without rebooting the computer into "true" Windows by using Apple's Bootcamp software. They both have modes where it "fakes it" and can run Windows applications
as though they were actually OSX applications (so they aren't inside the smaller virtualized Windows window). In order to use these applications, you need to purchase a copy of Windows (full version, not an upgrade license) and the virtualizing engine app, and then you "install" windows into the Virtualizing engine.
Since Apple computers are now just vanilla x86 (Intel) machines, the virtualized copy of Windows can run at essentially full speed. In the "old days" Macs could run virtual windows, but it was horribly slow and unusable due to the code translation.
I tried Parallels Desktop on my Apple MacBook Pro, but was very unhappy with how it worked. Mainly, I couldn't get MC to run in Coherence mode (the mode like I described above), it caused errors and issues with my network card in "regular" Windows mode, and I had external USB drive issues. My
main issue was that it was
completely impossible to uninstall from the Windows side if you didn't like it (and especially if you let the trial expire). I ended up having to wipe Windows off of my computer completely and reinstall from scratch because of Parallels, and that (to me) is completely unacceptable for trialware software. However, there were other things that I didn't like about it, and the support seemed terrible. (They seem to have the type of forum that we all reported we DON'T like in that "other" thread -- the ones where the developers don't listen, most posts have 0 or 1 responses, and there is an attitude of "you're doing it wrong" if you report that something doesn't work quite right.)