Do you have an old PC lying around gathering dust? How about a small-capacity USB flash drive sitting, unloved in a drawer? You can reuse your old computer and a USB flash drive by installing a tiny Linux distribution.
Mini Linux distros are great as they require fewer system resources than other options yet still deliver a whole operating system experience, and we have nine of the smallest Linux distros for you to choose from.
Reminds me of the fli4l project. Floppy ISDN for Linux. It used to be an entire Linux installation to use as a router that fit on a 3.5" floppy disc. I had it breath new life into an old 486 PC I had lying around.
Speaking of which, though it’s not Linux-based and I’ve never tried it, KolibriOS seems fascinating.