A window manager for the GNOME desktop. Basically, Metacity acts as a traffic cop that directs how a desktop window can be moved and resized, which program has the control of the keyboard, and how a window itself will look. Its author, Havoc Pennington, describes Metacity as follows:
It's a boring window manager for the adult in you. Many window managers are like Marshmallow Froot Loops; Metacity is like Cheerios.

Metacity is based on the GTK2 toolkit, the same kit that GNOME 2 is layered on top of. The window manager draws obvious comparisons to another popular GNOME window manager--Sawfish--but Metacity is much faster than the LISP-based Sawfish. Also, it appears that development on Sawfish has all but ceased.

On May 21, 2002, Sun Microsystems and Wipro Technologies announced that they were ending development on Sawfish and switching to Metacity. Reports state that the two companies made the swap because of Metacity's improved "accessibility, maintainability of the code, documentation, multi-head support and a general eagerness from the community" to contribute to it.

Additional development is still needed to work some of the kinks out of Metacity. A graphical configuration tool is still heavily under construction, for example. But now with Sun working on the project, these issues should be resolved very quickly. Metacity may turn out to be the window manger that thousands will use in their daily lives if it becomes the default manager for GNOME.