TopMod3d is a mesh modeling system that allows users to create watertight meshes. It is freely available, and open-source. My personal favorite was the chess set about half way through the video.

This is a collection of animations and renderings of models created using TopMod. The models and animations were created by students in the Computer Aided Sculpting course taught in the Department of Visualization at Texas A&M University.

via YouTube – TopMod Student Showcase.