This page maintains a list of academic, personal, and small non-commercial operating systems. For information regarding commercial or mainstream operating systems, please visit Wikipedia.

OSes have a high mortality rate: between 2004 and 2006, 112 of 213 OS Projects disappeared from the Internet. And looking at how often these projects are started by using the OS Project Announcement forum, in that same time period 68 projects were announced! The current total is 175 projects, but just 58 of them are active (as of January 1, 2018) and only 62 have been updated at least once since 2018 (three of which have been since abandoned), and 27 since 2019. Please help keep this list current by correcting it if you see any outdated information.

OSes without an update since 2015 are now located at Abandoned Projects.
More mature hobby operating systems can also be found at Notable Projects.
Particularly advanced and successful operating systems are listed at Advanced Projects.

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