Mac OS X: Having brightness, iTunes controls, and volume all right up in the function keys on your Mac is nice, but doesn't exactly leave them open for other functions. Micro app Palua lets you switch between standard and Apple functions quickly.
While you could always use the function key if you need to perform the odd "regular" F-key action, or even switch between Apple functions and standard functions in System Preferences, that isn't ideal if you use those standard functions a lot. Palua sits in your menu bar and lets you quickly switch between Apple and standard functions with the click of your mouse, or even a keyboard shortcut. That way, once you've got your brightness and volume where you like them, you can switch to normal function mode and use those keys to manage windows, launch applications, or do whatever you want.
Palua is a $US0.99 download for Mac OS X.