From 3D Tool USA:
The 3D-Tool Free Viewer can open and view STL files and native 3D-Tool files (EXE/DDD) 2D and 3D. It has a lot of the same features as 3D-Tool Basic and Advanced, such as Cross Section, Measure/Markup and Explosion. The 3D-Tool Free Viewer is a dynamic viewer for 3D and 2D CAD files. This gives you the ability to visualize, graphically analyze, measure and mark-up your CAD projects in 3D. The Free Viewer does not provide the ability to save your modificaitons or markup files; for that you would need one of the low cost paid versions: Basic, Advanced, or Premium version. The paid versions allow you to restructure assemblies, create exploded views, and animations using a very simple interface. Colaboration is easy, 3D-Tool produces zipped self-viewing executable files of your CAD projects, which can be e-mailed and displayed on any PC without pre-installation or licensing. The user interface allows anybody, without special CAD knowledge, to view your models, zoom in on details, or simply look inside your models using dynamic cross sections. Views from any angle can be printed or saved as pictures.