A bit of Linux and Mac payware has become free today (at least temporarily), following a pretty unusual marketing campaign in which Codeweavers promised to make Windows-API enabler & WINE GUI CrossOver free to customers for an entire day, if U.S. president George W. Bush achieved one of six goals proposed by the company.
If you already make use of a fully-Linux or fully-Mac environment, there isn't much room for a CrossOver offering. But if you find yourself making use of Wine quite often (which I do), their proprietary version is designed to run certain applications, such as the Microsoft Office suite, natively in Linux or Mac without fuss.
Due to incredible demand after the offer went up, their site has, of course, been brought to its knees. At the moment they have a barebones site in place that will still accept serial requests with which you can use to download the software.