Could have been any number of CAD programs.
for preference these days I'm using Qcad. You can also do similar things (as well as PCB layouts) using OpenOffice Draw. Qcad is more capable and will export DXFs; Draw is easy to use and fine for simple, non-CAD stuff. Take your pick.
Anyone else using Qcad? I'm going to buy CamExpert at some point soon as it allows very clean Gcode export from DXF files.