Ask HN: What is the tiniest FOSS code you've written that does something useful?

I would like to see publicly available free and open source code bases for very small projects--say a single file with less than 100 lines of source code--that also does something useful and caters to users. Have you written any such thing?

The smaller the source code the better!

I hope to see what kind of real problems be solved in such less lines of code and also pick some knowledge and practices from such code. Now of course many small projects may also have a large number of lines due to readme, license, test code, and such things but let us not count them for this discussion. Let us count the lines in only the actual program that serves the user (like things that are being invoked from main()).

This is not a request for code-golf kind of projects. But it is a request for projects that naturally turned out to be small or the ones which were never fully developed beyond PoC and yet turned out to be useful.