I know how to use Photoshop, and I wish 3D tools were as easy to use as a Photoshop. So I think that's the kind of app I want to create*. Not knowing what I don't know, I'm sure to stumble across features that no self-respecting modeling tool would add, but are great for people like me. That's the beauty of cross-domain knowledge, I guess.
Anyway here's a pen tool.
(*you know, if this ever actually becomes something I would want to ship and put my name to)