Win4Lin is software that runs on top of Linux and provides a guest operating system. It currently supports Windows 95, Windows ME, Windows 2000, Windows NT, and Windows XP. With Win4Lin, you run the entire Windows operating system, and you need to have a license for each copy of Windows. Because Win4Lin runs the entire OS, you can run *any* Windows application on Linux. The real value of Win4Lin is that it allows you to hang on to uncommon legacy applications as you make a transition to Linux. At this point, it's really not the basic office tools (such as Microsoft Internet Explorer and Office), or even the operating system itself, that keep organizations tied to Windows. It's the third party or custom in-house applications that prevent migration. Win4Lin allows you to make use of Windows licenses you already have to keep running those old VB apps. The Win4Lin technology is available as a terminal server as well.
Crossover Office is software that allows certain common Windows applications to be run on Linux. With Crossover Office, you don't need a license for Windows because you aren't running a complete operating system. A collection of the most common software is supported, including Microsoft Office, Quicken, Photoshop, and Visio. Crossover Office is a good solution for power users who require any of the supported applications. The Crossover Office technology is also available as a terminal server.