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According to the article: "it's any OS or application “under license terms that permit a recipient to copy, redistribute, and modify the software.”"

The article then explicitly cite "Debian, Fedora, Ubuntu, Arch, and the BSD family".

There is also another exclusion for libraries and software from a packages managers like apt and pacman.

So from my understanding ReactOS, hobby OS but also CP/M, FreeDOS, Haiku or Collapse OS...