There's an open-source modeler called NaroCAD that's been consistently developed by a core group. They've got a blog, narocad.blogspot.com where they post "nightly builds". It has a direct-edit workflow, faces are profiles that extrude and it has a well-integrated sketching that'll also extrude if closed. It's not unlike Autodessys's Bonzai3D. It's a lot of fun and probably a more intuitive modeler than AoI. It also has a command line and scripting potential, and a history tree which isn't really fully implemented yet, but has potential. It imports and exports IGES, STEP and BREP, so it can exchange with commercial CAD or with HeeksCAD and FreeCAD for conversion to stl. It's becoming the easiest open-source modeler to do something dramatic in.
