With the most recent Windows release, Opera made a "free" version available, as well as the standard US$39 version. The free version isnit actually free, but is rather "ad-ware." That is, users who opt for that version will constantly have a banner ad displayed.
According to the ZDNet article:
The Linux version of Opera 5.0 is in beta. The Mac version of Opera 5.0 is in internal alpha testing. A public Mac Opera beta--which will first be available for PowerPC-based Macs, followed by a version for older Macs--is expected shortly. A version designed for Mac OS X is also planned.
Both the Linux and Mac versions of Opera 5.0 are slated to ship this year, according to Opera executives. Hvistendahl declined to be more specific on availability targets, saying that the next two versions will ship when they are ready.
You can read the full story at the ZDNet Web site, and find more information about the Opera browser at the Opera Web site.