Documentation on the GAUGE API can be found here:
http://www.gauge3d.org/docs

You can also download the complete documentation in the following formats:

• Complete HTML archive: [ tar/gz, zip]
• PDF document: [ gz, zip]

Note that this documentation is not complete. However, many of the classe which are not documented are classes which are going to be removed and/or redone soon anyway.

Also note that GAUGE is far from done. There is still a lot of functionality that GAUGE doesn't have. These documents are here to give you a rough idea of how GAUGE works and some of the stuff that it can do.

If you have any questions, feel free to e-mail me.