When I’m in a tight spot and don’t have CAD software handy, there are a couple of sites I use to view CAD files online.

ShareCAD lets you upload CAD files in a lot of different formats and displays the 3D model. It offers very minimal interaction, but you can pan and zoom. You also get a link that you can share via email with collaborators so that they can view and download the file. Handy.

ProfiCAD’s AutoCAD Viewer is more limited, but sometimes works where ShareCAD doesn’t. For example, here is an AutoCAD drawing that ShareCAD couldn’t handle.