Look into toybox. It's a tiny reimplementation of GNU coreutils that ships in Android.
The author was on the core team for another project in that space (I think busybox). He saw first hand how copyleft sounds good but ends up being lots of friction with no practical benefit, and vowed to public domain all his projects after that. BSD0 is him giving a name to a public domain grant so OSS people could recognize it.
https://en.wikipedia.org/wiki/John_Carmack#:~:text=The%20sou...