Debian

Debian is one of the oldest Linux distributions still actively developed, run entirely by a global volunteer community under its own Social Contract and Free Software Guidelines rather than a company, with a famously deliberate, consensus-driven release process. Its 'Stable' branch is the backbone choice for servers that need to run untouched for years with only security patches, while 'Testing' and 'Unstable' branches offer newer packages for those who want them. Its outsized influence comes less from direct desktop usage and more from being the foundation an enormous share of the Linux ecosystem builds on -- Ubuntu itself is a Debian derivative, several layers removed from many of the distributions in this very directory.