My most favourite open source application QCAD is now at version 3.
I buy a license for the “Pro” version because it’s just a fantastic easy to use product.
At my $DAYJOB today I found out QCAD 3 (I was using RC5) can open dwg files so now it’s as useful to me as the $1000AUD+ AutoCAD LT
The new features of QCAD 3 mean I’m happy to recommend it.
So if you want a cross platform (Linux, Mac, Windows) simple to use DXF/DWG file editor try QCAD 3 from http://www.ribbonsoft.com/en/