How do I open the files hosted on this site?
You will need a CAD program to view these files, such as FreeCAD.

I am getting the message “This file is invalid for use as the following: Certificate Trust List”
Open your CAD program and then browse to the CAD file and open it. Read the detailed answer here.

What is a RepRap 3D printer?
You can watch this YouTube video to get a general overview of how 3D printing works and demonstrate the actual printing process. You can read about them at www.reprap.org

How can I support DEFCAD?
Go here and donate to Defense Distributed.

The downloads are slow, any alternatives?
Yes, download the MEGA PACK torrent.