Debian.

Stable and free Linux distribution, basis for many other distributions

Facts

Alpine Linux
Lightweight and secure Linux distribution, popular for containers and embedded
AT · open-source
↗
EndeavourOS
Arch-based Linux distribution with accessible installation and community
NL · open-source
↗
KDE neon
Linux distribution with the latest KDE Plasma desktop on Ubuntu basis
DE · open-source
↗
Linux Mint
Irish open-source Linux distribution focused on ease of use
IE · open-source
↗
Mageia
Community-driven Linux distribution originating from Mandriva
FR · open-source
↗
Manjaro
Arch-based Linux distribution with user-friendly installation
DE · open-source
↗
NixOS
Declarative Linux operating system with reproducible system configuration
NL · open-source
↗
openSUSE
German Linux distribution with choice of Tumbleweed (rolling) and Leap (stable)
DE · open-source
↗