There are versions for Windows, Macs, and Linux. The Linux version comes in the native format for just about any distribution you can think of.
I've played with it a little bit tonight, but only enough to verify that it is different than Firefox. Not better than, nor worse than, just different. If I play with it more, I'll write up a bit of a review, but at the moment it's probably only something to bring up when Firefox just doesn't want to work on a given web page.
If you're a Windows user currently using IE, you might want to try Opera. If you're already using Firefox, try Opera if you want, but don't (please, oh, please, don't) go back to IE.