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Multics - Unix's father
TUHS - The Unix Heritage Society
The Open Group - Owners of the Unix Trademark
Dennis Ritchie Home Page
Retrocomputing Wiki
FullUnix.com
IBM Home Page for AIX
Home Page for Oracle (formerly Sun) Solaris
HP-UX Home Page at hp.com
RedHat Linux
OpenSUSE Linux
NetBSD
FreeBSD
OpenBSD