Linux (Ubuntu): If you want to tweak Ubuntu's Unity interface more to your liking, the Unity Tweak Tool is for you. It gives you everything you need to make your desktop truly yours.
Ubuntu has a lot of tweaking tools, but Unity Tweak Tool -- formerly known as Mechanig -- brings more Unity-focused tweaks to the table in a very easy-to-use interface. Its set up almost exactly like Ubuntu's main System Settings windows, but with settings that aren't as easy to find, such as customising hot corners, workspaces, scrolling tweaks, and theming your fonts and icons.
To install it, just run the following commands in a terminal:
sudo add-apt-repository ppa:freyja-dev/unity-tweak-tool-daily sudo apt-get update && sudo apt-get install unity-tweak-tool
Unity Tweak Tool currently only works in Ubuntu 12.10 and higher.