Localghost is a simple status menu thinger to make it so that you can set up a set of hosts that you use for development and quickly point them to localhost.
Once Localghost starts you'll see a preferences menu where you can add the hosts that you use for development. Once added they'll appear in the Localghost status menu and can be turned on and off with one click (well, almost, it'll ask for your password once per session).
There are screenshots and whatnot at the Localghost homepage.
Localghost is Copyright © 2010 Scott Wheeler and available under the GNU GPL.