Here is the url for a project that I have really gotten into over the last year:

http://code.google.com/p/heekscad/

This project is really separated into a series of smaller bits that can all be put together to make a total open source CADCAM solution. HeeksCAD is the main engine for all the other libs. You can add these other libs to make it do more:


HeeksCNC- is the main plugin to make profiling gcode
http://code.google.com/p/heekscnc/

once you install HeeksCAD and then get HeeksCNC set up as a plugin, then you can add more libs for doing pocketing, adaptive roughing, and surfacing in 3D:

libarea (pocketing):
http://code.google.com/p/libarea/

libactp (adaptive roughing of pockets- high speed roughing):
http://code.google.com/p/libactp/

opencamlib (Ander's Wallen's 3D surfacing libraries):
http://code.google.com/p/opencamlib/

HeeksPython- let's you do some parametric design work in python
http://code.google.com/p/heekspython/

HeeksArt- this let's you do some Blender like editing of surfaces
http://code.google.com/p/heeksart/


I think the genius of Dan Heek's approach was making it easy to add libraries to his main program.

The main thing that one needs to get started is to have the Opencascade libraries set up on your system. These libraries seem to be a gift from the geometry gods that let developers get up to speed with professional CAD programs fast.

I've been working with HeeksCAD lately. Dan Heeks has created a very impressive open source CADCAM platform.
You can get the sources or binaries here:
http://code.google.com/p/heekscad/