Window Maker is an alternative to the Gnome Desktop. The real purpose of Window Maker is to explore an alternative to the heavy weight Gnome which uses a lot of resources from your machine. How much, well in a test we did with Window Maker we found that it used only 4.5% of the resources, RAM and CPU, that are typically used by Gnome, a very significant difference.
Here is a list of Resource Comparison with other window managers that you could use.
Gnome is a hog, it uses a lot of resources. If you would rather save your resources for a faster more efficient Desktop test out Window Maker. For directions on how to test out an alternative Desktop CLICK HERE.
Window Maker can run any of the applications you have installed on Ubuntu. It is highly configurable, lightweight and great looking.
A great source of information for Window Maker can be found at the site. Here is a project that has documentation that will help you use Window Maker efficiently.
Here is a link to the User Guide