Learn how to use your terminal to create 3D models using stl_cmd, a suite of tools that can generate, inspect, and manipulate STL files.
I've read that dowel joints are nearly if not as strong as mortise and tenon joints. The mortise and tenon joint requires expensive tools (specifically a table saw and a router) and the know how to make them, but dowel joints can be made with just a drill. The tricky part, though, is getting your dowel holes lined up on each piece. With my dowel jig widget, you can configure a jig for your specific situation and 3D print it at home or for an affordable price online.