Tiny Core is a very interesting distro, giving you the bare minimum Linux install to then build upon as you see fit. It may be a little tricky for newer users to get their heads around, but more veteran users can make Tiny Core works exactly as they wish. Either way, Tiny Core would make an excellent addition to the distros available on Raspberry Pi.
This has now happened thanks to piCore 5.1. Based on Tiny Core 5.1, this official port of the distro to Raspberry Pi. The base image is just over 20 MB, and loads into RAM like the main version of the distro.
You can grab the new image from the Tiny Core site now, and make yourself a highly optimised Raspberry Pi OS.