These days, for the situations in which I want to make my own distro, I go to [buildroot]. I recently (well, 2 years ago) built an image to replace DOS on a Pentium 75 system. Built an small distro containing nothing more than a a couple users and minicom, with minicom attaching to the serial port, and ssh access. Sure, I could have done this with a raspberry pi and a usb serial adapter, but this was more of an educational side project. I was already re-using the PC power supply and case to power a standalone APRS setup, and figured I should be able to re-use the computer and serial port to provide remote access.

[buildroot]: https://buildroot.org/