dxf

Mesh Lab

gtoledo3's picture

http://meshlab.sourceforge.net/

What I'm finding to be really useful:

-Straightforward conversion between many 3d file types, particularly 3ds, obj, and collada, but having OFF, DXF and some of the others has proven useful as well.

-A decent smoothing tool that's speedy and barely makes the file larger/more complex.

-Surface reconstruction from points (so it can take some more obscure data types).

-Tools to automatically clean up models - remove duplicate faces, inner faces that are unneeded, hole filling, etc.

-Really quick texturing/paint on mesh tools.

It's not extremely full featured, but what it does, it does solidly and I haven't encountered any problems with it. The fact that it's free and open source is a plus too.