ALCustomTabBarController is a project mainly written in OBJECTIVE-C and C, it's free.
Custom UITabBarController for use in iPhone applications.
ALCustomTabBarController is an iOS 4.0 project that allows customization of the standard UITabBarController such that the UI can be modified from it's standard iOS look and feel. The implementation should not be considered production-ready, but should instead be taken as an example of how one might customize the UITabBarController
ALCustomTabBarController is iOS4 and iPad compatible and released under the MIT license (see ALTabBarController.h).
This is not a static library, but instead a demo application utilizing the two main classes which make up the custom UITabBarController: