I'm the author of OpenSCAM. I've just released a new version which has a much improved user interface, in one window instead of two and using Qt. There are also some bug fixes and it now works on OS-X.
If you have any problems with this software please open an issue on the GitHub page: https://github.com/CauldronDevelopmentLLC/OpenSCAM Or email me directly.
OpenSCAM v0.2.3 beta
Open-Source software which can simulate 3-axis NC machining