Mac: Snap is a tiny little app that automatically assigns keyboard shortcuts to the first 10 items in your dock, making it easy to launch them and switch between them via your keyboard. Additionally, you can manually assign keyboard shortcuts to any other app beyond the initial 10, whether it's in your dock or not.
To use it, all you have to do is launch Snap and press anything from Command + ` to Command + 9. (Command + 0 isn't an option for some reason.) This will either launch the corresponding app if it's closed, focus/show it if it's open, and hide it if it's the app that's currently in focus. You don't need to set anything up to get Snap working, but you can alter its functionality and add new shortcuts manually by selecting Preferences from its menubar icon. If you don't like the default shortcuts and want to change them a bit, this is where you do that.
That's pretty much all Snap does, but it's handy if you like to navigate via the keyboard and you find OS X's built-in app switcher a little too slow.
Snap ($US) [iTunes App Store]