My weekly submission, a unit conversion calculator, can be found here on my website. It can convert units of length, area, volume, speed, mass and angle, with 97 total units, and 6 significant figures of accuracy for every single one! And, of course, there is an API as well. ;)
Please ignore the repl I have attached to this post as it is the entire repl for my personal website, which I have already shared in a different post. The links to the source code for the converter are specific files in that repl.