Mac: You can set up gestures on your MacBook to make navigating with the trackpad (or Magic Mouse) a breeze, but the default selection has its limitations. Jitouch is a utility that adds a bunch of useful gestures for browsing the web and using different software.
Similar to the previously mentioned MagicPrefs, jitouch allows you to customise gestures to quickly open software and do just about anything in your browser. Jitouch has a different set of gestures to select from than MagicPrefs, but it also has character gestures. With these, you can draw out a letter to perform certain actions, such as a "B" to open your default browser or "O" to open a new document. It ends up powering up your trackpad in a lot of ways, and it's especially useful when you don't have a mouse on hand.