Mach3 is the flagship of the ArtSoft products. It is released in two versions: a Lockdown version, and a Development version. The Lockdown is a stable, static release recommended for new users, or people trialing the software. The Development version contains developing features and is released quite often so people can obtain new (but untested) features and capabilities. Both releases are limited to 500 lines of Gcode until licensed. Mach3 has a limit of 10,000,000 lines of Gcode even after licensing.
GCAM is the free GNU Computer Aided Manufacturing package. Most 3-Axis Computer Numerically Controlled (CNC) mills such as the Taig and Sherline are supported in both english and metric units. GCAM also imports RS274X (Gerber) and Excellon drill files for gerber to G-code pcb milling conversion used in circuit board prototyping.