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.
CodeShark Mill is a hybrid CNC code editor with built in cad/cam/dnc functionality. Codeshark includes DNC communications, full editing, an integrated Cad system as well as a unique feature set not found in other programs. CodeShark is affordable for the individual machinists and multiple seat discounts make it economical for machine shops as well.