Mac: If you want to change the inner-workings of OS X, you typically need to dig into Terminal commands or download a bunch of special software. MacUtil is an app that makes customisation simple by providing you with all sorts of tweaks in a simple menu.
MacUtil is similar to something like Lion Tweaks, but it has a few more options to choose from. For example, you can go through and remove warnings when changing file extensions, allow text selection in quick look, and force apps to save to the disc and not iCloud.
MacUtil doesn't have anything you can't do with a good list of Terminal commands, but if you don't feel like messing about in Terminal, MacUtil is a simple way to customise your Mac as your heart desires.