Pow and Anvil

Pow is a zero-config and super easy to setup rack server for Mac developed by 37signals. Besides being easy to use, it enables you to have multiple Rails apps¹ running simultaneously, without having to remember all those pesky ports, by giving the app a hostname based on a symlink you chose and a .dev extension.

And Anvil makes Pow even easier to use. Just open it up from your menubar, point it at a folder, type in a name and the pow server is running.