Ruler: A straight-forward, general-purpose build tool written in Rust. Home page here:
PovRay is an open-source raytracer with its own scripting language for describing scenes. It can be used to render beautiful images and animation. It is a dinosaur, but also, there is no modern software quite like it. Some example images here:
is a webapp that only does one thing. Drag a file onto it, the file uploads, and you receive a download link that works for at least ten days. Here's the cool thing, though: before the upload completes, you already know what the download url will be, because it's based on the sha512 of the file contents. That has to be useful for something.