Redecorating an old house from the 1920s requires a bit of work. Instead of drawing and redrawing our new bathroom over and over, I rummanged the web for a GPL Linux CAD program, and lo and behold, qcad came to the rescue!
Qcad started off as a small 2D CAD program and is still that; a 2D CAD program. It's not that small anymore; it took a while to compile! Based on my experience with computer aided design; which is basically a year at college; the application seems to go quite far in offering what CAD programs offered to professionals back in the early '90s. The professional CAD market has of course moved on to 3D modelling tools, but they are cumbersome to use if all you want is to replace your paper with a computer. You still get to do the thinking.
Best of all, qcad is GPL, and 4Mb of source is available to compile; and a commercial version is available with support for polylines and scripting.
For my bathroom, I think I can do without polylines and scripting. Interestingly, qcad uses DXF as its native interchange format, and has a load of parts which can be downloaded and used. I don't need to draw a sink, a toilet, door! All those complex parts are ready-made.
It of course supports layers, so I could in theory draw the electrical wiring as well, and give the contractor several printouts, one for the electrician, one for the plumber and so on. (Note to self: just make sure they're using the same version of the plans!)