Hi, I have Rhino and a trial version of RhinoCam. I have spent a lot of time on the telephone with a RhinoCam representative and he is most helpful even though I have told him that RhinoCam is too expensive for me.
RhinoCam has the advantage that it is a plug-in for Rhino which makes it very attractive to use. You can go back and forth between your design and the CAM portion from the same user interface.
The RhinoCam trial version will not let you save a full G-code solution, but the rep says that the trial version using their FreeMill product will allow you to generate and save a finish toolpath so that you can test it on your machine.
As Alan says, each CAM program generally has a selection of Post Processors that handle the machine specific commands. You can generate your own Post Processor to use in RhinoCAM if your machine is not supported by the RhinoCAM distribution.