While I already mentioned Netfabb in an older post I recently started using the Studio Basic free version for our Fabbing exercise.
- The Studio Basic version is limited but free.
- It is cross-platform, which wasn't the case when I first mentioned this software, IIRC.
While I assume that Magics from Materialise is still the software king for STL repair, it comes at a cost and only works on Windows, so maybe you can give this software a try.
The video below gives a very simple example of viewing and automatically repairing a 3D STL model from SketchUp, exported using a free script, from http://forums.sketchucation.com/viewtopic.php?f=57&t=8447
Simple STL repair using NetFabb Studio Basic from Stefan Boeykens on Vimeo.
A fairly simple model, made in SketchUp 8 Pro using the Solid Tools and exported to STL using the su2stl.rb ruby-script. As you will see, this model has some (minor) issues; such as missing face and some open edges. The free version of NetFabb Studio Basic is able to automatically repair them.
Oh, this works on Windows and on Mac, which is quite uncommon for such software. (There is no audio with this video)