iScroll2 is a modified trackpad driver that adds two-finger scrolling capabilities to supported pre-2005 PowerBooks and iBooks on OS X 10.3 and up.

Supported models include most aluminum PowerBooks introduced from 2003 to 2004 as well as most G4 iBooks.

Note: Models that have two-finger scrolling already built-in are not supported! These use a completely different, USB-based trackpad, the driver or which is not available as open source.

Models that are known not to be supported include all G3 and Titanium PowerBooks, the very first 12" PowerBook model, all G3 iBooks, and all newer machines that come with two-finger-scrolling built-in: The trackpads of the older machines simply lack two-finger detection capabilities completely, whereas the models that have scrolling built-in use a completely different, USB-based trackpad, the driver for which is not available as open source.

Requirements:
OS X 10.4-10.5
PPC