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.
Or static HTML sites like your octopress blog. ;) ↩