GNU Emacs is a customizable text editor that is an interpreter and dialect with extension to support text editing with content-sensitive editing modes, built-in documentation, Unicode support, and more.
FreeCAD is a parametric 3D modeler made primarily to design real-life objects of any size.
GNU Octave is an open-source mathematical modeling and simulation software very similar to using the same language as Matlab and Freemat.
OpenSCAD is a software for creating solid 3D CAD objects.
LibreCAD is a free Open Source CAD application for Windows, Apple and Linux.
Make is a tool which controls the generation of executables and other non-source files of a program from the program's source files.