KDE 4 funciona sobre Mac OS X

(Disclaimer)

They may not work. They may not even install. They may make your monitor explode in a shower of glass. EVEN LCDs! They may make your children grow horns, and cause the people in your neighborhood to explode spontaneously while doing the Macarena. They will rip out your eyeballs, and eat your soul with a really dull spoon, laughing and cackling while forcing Cheerios up your nose. They will make your intestines explode in a rain of confetti, while evil clowns bite your feet.
[edit]
But Actually, It Kind Of Works

OK, so now that I've got that out of the way... Let's just say this stuff is still very alpha. If you want to try things out, go ahead, but it's still very early for bug reports. If you have issues, please see the "Development" section below to contact the KDE/Mac developers.

However, some apps work enough to be usable (especially simple things like KAsteroids and KWrite) and other apps work enough to play with them and try them out. Give it a shot, you may be surprised.