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.

Because there aren't too many touch-enabled devices so only a few people can enjoy the touch functionality in Unity (Ubuntu 10.10 Netbook Edition), the guys at Canonical blog posted a video showing off the amazing multi-touch capabilities of Unity: