I don't know of any that are open-source. Are you looking specifically for something free, or more something that will let you tweak and play with the code? I use AutoCad myself (use it at work daily), but that's not what you're looking for. Maybe research the progs that are available to Linux OS's - their stuff tends to be more open-source friendly.
Cheers!
I just saw your pictures from the wreck, Architect. Jeez, it's sobering to see that kind of stuff. Glad that you have recovered and are back on the road, though! I noticed you've got some nice orthographic drawings in your posts. I'm looking for a good open-source CAD program, it doesn't have to be fancy, have you come across any?
I continue to appreciate the positive reinforcement about my build. It started out wtih just me wanting to photograph what I was doing and share all of it, whether it worked or not, just so anyone interested could use it as a learning experience. I over-think and over-research everything, so I dug deeply into the knowledge here, in our SOHC community.
And I'm working on multiple CB350 twin projects right now, including my first bobber-type build. I inherited a free partial bike that included a partly cut-up frame. So, I said "why not cut it up more?" I'll get some pics up here, soon.