I designed an entire theatre using QCad Pro ; architect was on some unlicensed, outdated AutoCAD and engineering on Vektorworks. But for engineering, which I had to require .dxf exports from, I was able to work, integrate and send back to everybody from QCad. QCad is free and FOSS, the Pro version is $40/year and offers more import-export format and some neat scripts. If you don't want to fork out the $40, ODA File Converter will do the .dwg-.dxf conversions for you.