STLViewer
STLViewer is a free cross-platform viewer of STL files.
If you want to send bug reports or feature requests, please submit them to the github issues and pull requests pages respectively.
Icons are partly retrieved from the Font Awesome icon set.
Screenshots

Installation
Get the source
Clone the git repository:
git clone git@github.com:cravesoft/stlviewer.gitInstall dependencies
For Ubuntu, simply enter the following command that will install all necessary packages:
sudo apt-get install libqt4-dev libqt4-opengl-dev qt4-qmakeCompile
qmake && makeThis will generate an executable called stlviewer.