LinuxCNC is a software system for computer control of machines such as milling machines, lathes, plasma cutters, cutting machines, robots, hexapods, etc.

LinuxCNC is Free software released under the terms of the GNU GPLv2 (General Public License version 2).

LinuxCNC is a descendent of the original NIST Enhanced Machine Controller software, which is in the Public Domain.
LinuxCNC has many exciting new features and brings a lot of new functionality (a flexible and powerful Hardware Abstraction Layer that allows you to adapt it to many kinds of machinery, a software PLC controller, easier-than-ever installation, a new trajectory planner, and more.)

LinuxCNC is precompiled with Ubuntu LTS (long term support) versions for ease of installation and longevity.

http://www.linuxcnc.org/

http://wiki.linuxcnc.org/cgi-bin/wiki.pl