radmesh

https://github.com/admesh/rubygem-admesh

ADMesh is a library for processing triangulated solid meshes. Currently, ADMesh only reads the STL file format that is used for rapid prototyping applications, although it can write STL, VRML, OFF, and DXF files. Those are bindings for Ruby. You'll need the ADMesh C library in version 0.98.x.