Vismach is a simulator to show 3D previews of a physical machine. It's supposed to be a quick hack and as such doesn't have any documentation. The source on git is in [lib/python/vismach.py] and the models on git are in [configs/sim/axis/vismach/]
here are some screenshots:
vismach can be used to verify motions that don't show up in AXIS preview, such as custom kinematics or m-codes
this screenshot shows a "virtual rotary table" using the C-axis
Another example on what one can do with LinuxCNC (ex Enhanced Machine Controller) and Vismach help.