Some time ago during evening googling i have found interesting special CAD for bikes called RattleCAD.
Here is their project page on SourceForge: http://rattlecad.sourceforge.net/index.html it is free and open source software.
And couple of their screenshots. Interesting to hear from bicycle fans some opinion about this software.
A bit unusual that it is written on TCL language.
Interesting as well, is there any other software like that?