Opera

A cross-platform Qt-based browser.
Aims to be very fast and lightweight.
Commercial. Distributed as binaries for most common platforms. (Ad-ware or pay)
Support for some W3C standards (or parts of them) is not present. They may or may not be added in the future.
Very small marketshare. (sort of falls between the chairs of OS-shipped browsers and the open-source Mozilla).

Verdict

Test with it, if you can (and you probably can). Other than that, it's not a very important browser. (at least not todate)