Quote -
Hexagon is abandonned and free.
www.anim8or.com is also free.
Also abandonned and free, but less powerfull and has no symmetry, but another free 3D app.

I think Silo is still "to pay for"?.

Yep, but Silo also appears to be in the abandoned category. :(

I also think Silo would be a great way to introduce people to modelling. :)