TCW, which is used by absolutely no-one else and is proprietary. Recently I've needed to produce slightly more complex drawings for items to be sent for laser cutting and was hoping to be able to send my requirements by email using a file format that interfaced with their laser cutting software.
I've been using TurboCAD for many years to produce simple technical drawings to be printed out for bits and pieces I want fabricated and by and large it's worked pretty well.
