Windows: We recently detailed two ways of getting Mac-like multi-finger scrolling on a Windows laptop, involving little open-source apps and hacked drivers. Touchpad giant Synaptics actually offers its own app, Scrybe, that provides multi-finger scrolling, along with gesture-style application launching.
The big catch to Synaptics' own Scrybe app is that it's fickle. You need to have a Synaptics touchpad on your laptop, you need Synaptics-approved drivers installed, and, depending on your hardware/software setup, Scrybe may or not play nice. On my ThinkPad T61p, I installed Scrybe after removing my hacked drivers and TwoFingerScroll app, and I did get two-finger scrolling and three-finger motions working. The settings interface, though, had graphical and display problems, so I couldn't quite guess at what gesture I was setting my different applications to launch with.
Others, however, have had better luck with Scrybe, getting the kind of "write an 'a' with your finger to launch Amazon.com" experience detailed at Scrybe's web page. There will likely be a follow-up post here about Scrybe's offerings, but in the meantime, you can check it out yourself, if you'd like scrolling and gesture powers without having to make slightly grey-area moves. It's a free download for Windows systems with Synaptics touchpads.