Touchégg is a multi-touch gesture recognizer for Linux (released under GPL) that allows you to associate actions to multi-touch gestures. It can be used to assign gestures to actions like maximize or minimize windows, resize windows, show the desktop, emulate all mouse functions and more.
The application was initially designed for Egg Window Manager but José Expósito (the Touchegg developer) decided to extend its functionality and made it compatible with any window manager.
Touchegg should work on any touchpad compatible with uTouch but its wiki currently only holds the configuration for Apple Magic Trackpad and Asus eeepc 1000h (Buildin Elantech Trackpad) (though the configuration should be similar for other devices too).
To learn more about Touchegg (as well as how to configure it), check out the video below:
Download Touchegg (includes Ubuntu .deb - unfortunately for 32bit only). Please note that I do not own a multi-touch device so I couldn't test Touchegg.
Thanks to José Expósito for the tip!