As much as some of us don’t like it, building things for real requires some mechanical component. Maybe it is something as simple as an enclosure or even feet for a PCB, but unless you only write software or play with simulators, you’ll eventually have to build something. It is a slippery slope between drilling holes for a front panel and attempting to build things that move. Sometimes that’s as simple as a hinge and a spring, or maybe it is a full-blown robot articulated arm. That’s why [RectorSquid] built Linkage, a “program that lets you design and edit a two-dimensional mechanism and then simulate the movement of that mechanism” (that quote is from the documentation.
The program has had a few versions and is currently up past 3.15. To get an idea of the program’s capabilities, the first video below shows an older version simulating a ball lift. The second video shows the actual mechanism built from the design. The associated YouTube channel has more recent videos, too, showing a variety of simulations.