Torque: Linux is the Core. The thing you see is actually the User interface, you can also run linux in console mode without.
the most common ui are KDE and Gnome, but there are also some which show your PC in 3D, so you can be the player in your filebrowser etc where each directory is a door etc
However, most of the UI are fast and ready for user customization.
But on the other hand, there are some with memory leaks bringing Linux to Windows level *bah*