Just came across this today. Perhaps it has been linked to before, but it probably deserves a second go 
“Teddy is a sketch-based 3D modeling software. You can make interesting 3D models just by drawing freeform strokes.”
I had a go with it and it looks like a useful little adjunct to ZBrush. It sort of seems like a cross between alpha skinning and zspheres and felt like a really nifty way of sketching a mass that can be imported into ZBrush, skinned and further worked on.
The ‘Teddy’ program saves models as obj files, although the newer version (Smoothteddy) saves files only in the ‘asg’ format for use in Alice, another freeware program designed “to provide the best possible first exposure to programming for students ranging from middle schoolers to college students”.
It’s really fun to use too and would be ideal for kids as there are very few actual controls. And it’s free.
He also has some little programs for making cloth and architecture, but I have yet to play with these. And if you’re really bored you can run it in your browser at work