This might not be quite what you're looking for, but I built a 3D modeler myself. I designed it with a programmer's needs in mind, rather than an artist's, because Blender makes no sense to me.
Basically, you write Java source code that builds the model. All you need is graph paper, a pencil, a colored pencil, and a ruler.
It might help you with the creation of new models, but not with the modification of existing models.
Currently, it doesn't support any kind of 3rd party model import/export, as this isn't a feature I actually need for my project, although it is something I've thought about adding many times. File parsing is a pain... I'd be happy to accept submissions in this area, BTW.
Edit: Forgot to give you the URL:http://deimosproject.sourceforge.net