VirtuaWin is an Open Source, virtual desktop manager for Windows which can organize applications over several "virtual" desktops.
A virtual desktop manager lets you organize applications over several virtual desktops (also called 'workspaces').
Virtual desktops are very common in Unix/Linux, and once you get accustomed to using them, they become an essential part of a productive workflow.
VirtuaWin is designed to be simple and elegant to use yet still be highly configurable and extensible.
For example if you use two virtual desktops you can put a Web browser on desk 1 and by using a desktop manager "switch away" the Web browser and it will seem like you have a new empty workspace (desk 2) to put another application/applications on.
The program supports up to 20 desktops, configurable key/mouse control, user defined icons, modules for additional features, and much more.
Download it here.