Pow is a zero-config Rack server for Mac OS X. Have it serving your ruby rack apps locally in under a minute. It is compatible with rbenv automatically and no additional step is required.
Let's say you're working on an app that lives in ~/Dev/datapipe-awesome-app. You'd like to access it at http://datapipe-awesome-app.dev/.Setting it up is as easy as to add a symlink of your app root folder into ~/.pow
cd ~/.pow
ln -s /path/to/myapp
That’s it! Your app will be up and running at http://datapipe-awesome-app.dev/