Simple user front-end

I'm looking for a simple open source CAD/CAM front-end - something like Rhino. It looks as if Open Cascade (or 3D Workbench) has all the primitives to produce very powerful and complex CAD/CAM packages - as the screenshots show!

Has anybody put together a simple front-end? I'd imagine that there must be something like this around if only as a test-bed for the calls.

Where would I find this?

Alternatively, is there a linux or other front end to Open Cascade that either works or is in Beta that you could recommend?

Just as an aside, is there a standard NC protocol and does Open Cascade support it? You can see that I'm new to all this...