Open Source STL Viewers

Linux / Mac / Windows

GLC_Player

http://www.glc-player.net/ :  An open source software used to view 3D models (COLLADA 3DXML OBJ 3DS STL OFF COFF Format) and to navigate easily in these models. English and French interface.

Gmsh

http://www.geuz.org/gmsh/ :  A 3D finite element grid generator with a build-in CAD engine and post-processor.

Meshlab

http://meshlab.sourceforge.net/ :  Both a viewer and a very powerful mesh editor. Meshlab supports a very wide range of 3D file formats.

Linux / Windows

Viewstl

http://sourceforge.net/projects/viewstl/ :  An open source way to view Stereo Lithography Files as shaded on-screen images. Ascii STL files and dynamic rotation, scaling, and panning are currently supported.

Windows

EasyViewStl

http://www.gcad3d.org/EasyViewStl.htm :  Simple but lightweight and fast viewer. Unfortunately only available with German interface

MiniMagics

http://software.materialise.com/minimagics :  Can also analyze and section parts. English, German and Japanese versions.

VisCAM View

http://www.materialise.de/fusion-von-marcam-engineering-und-materialise-gmbh : A very easy-to-use and efficient tool to view, check, measure and communicate STL files. Visualisation of STL, 3DS, VRML, DXF, PLY, ZPR and VFX files.