STL-Viewer STL Files: STL (an abbreviation of “stereolithography”) is a file format native to the stereolithography CAD software. Nowadays STL files are widley used within 3D-Printing technology. Purpose: As there is no build-in support to preview STL files for the Windows-Explorer (as far as I know…), I implemented this utility program for only this reason. The software is self dependent and consists of one single executable. The program emulates a local web server and therfore requires an up-to-date web browser installation (iExplorer, Safari, etc…).