This free software was originally created by Matthias Garzarolli. Guidemaster is included in System Utilities.
From the developer:
Guidemaster is a tool for the automatic tracking of a telescope on a equatorial mounting by USB-Webcam.
Supported cameras for guiding: webcams, SC1,SC2,SC3 modified webcams, Meade LPI camera, all cameras, which either supports VFW or DirectX, shoestring USB adapter for modified webcams, serial interface for modified Webcams, Trifid Nugget Camera from Yankee Robotics and more.
You may want to check out more software, such as Alignmaster, which might be related to Guidemaster.