Well, Apple has that functionality built into OSX as well. It’s activated using the Command + Tab keys. Press them together once and it activates the Application Switcher.
If you hold down the key and continue to press it, a block highlights the application that becomes active when you release the key combination.
Apple adds another cool feature to the Application Switcher. If you highlight an application and press the Q key, it will quit that application. Also, if you highlight an application and press the H key it will hide that application.
The Application Switcher is a great way to quickly move between your running programs. If you have any other interesting shortcuts, discuss them here.