Librecad: Cad software to do some 2D work.
Heekscad and heekscnc: CAM and CAD software. Use it to generate gcode with 2D and 3D files.
Pycam: gcode generator
F-engrave: vcarving tool. Slow but good results.
Freecad: new 3D software. Early stage of dev but you can do a lot with it.
Pcb2gcode: get code to engrave your PCB for electronics projects.