This is a custom container view controller for iOS 5 that works just like a regular UITabBarController, except the tabs are at the top and look different.
This is a fork of https://github.com/hollance/MHTabBarController. It uses Quartz to draw the view instead of using images. It also allows you to position the arrow indicator up or down.
To customize the tab bar's appearance you currently have to mess around in the code a bit.
The MHTabBarController source code is copyright 2011-2012 Matthijs Hollemans and is licensed under the terms of the MIT license.