On a more serious note: We're currently working on an interferometer for measuring the nanometer-scale displacement by the piezo stack actuators of our scanning tunneling microscope (STM). To do this without budget, we started working on a 3d-printed system of optomechanics, all designed with @FreeCAD. It works surprisingly well! We'll publish the designs soon, including measurements of their stability performance. You can read more about the project(s) here: https://wiki.fa-fo.de/projects:optics:start