A controls engineer I know designs systems using ladder logic diagrams, which represent the control logic graphically, largely by drawing the relays and other d

A controls engineer I know designs systems using ladder logic diagrams, which represent the control logic graphically, largely by drawing the relays and other devices that an earlier generation of engineers would have wired up physically. http://en.wikipedia.org/wiki/Ladder_logic http://en.wikipedia.org/wiki/Ladder_logic In the systems dynamics world, programs like Simulink, ModelicaML, and Stella allow users to graphically assemble the systems they want to simulate, by linking icons (e.g., "accumulators" and "flows"). http://www.mathworks.com/products/simulink/ http://www.mathworks.com/products/simulink/ http://www.iseesystems.com/softwares/Education/StellaSoftware.aspx http://www.iseesystems.com/softwares/Education/StellaSoftwar... http://www.openmodelica.org/index.php/developer/tools/134 http://www.openmodelica.org/index.php/developer/tools/134 None of these cases really meets your criteria that the source code cannot be expressed as text. Rather, they all use graphics to enable non-traditional programmers (e.g., controls engineers with legacy skills) to interact with a modular programming system.