The following is some of the well-known Unix flavors, with links to their official home pages.
AIX – IBM
BSD/OS (BSDi) – Wind River
CLIX – Intergraph Corp.
Debian GNU/Linux – Software in the Public Interest, Inc.
Tru64 Unix (formerly Digital Unix) – Compaq Computer Corp.
DYNIX/ptx – IBM (formerly by Sequent Computer Systems)
Esix Unix – Esix Systems
FreeBSD – FreeBSD Group
GNU Herd – GNU Organization
HAL SPARC64/OS – HAL Computer Systems, Inc.
HP-UX – Hewlett-Packard Company
Irix – Silicon Graphics, Inc.
Linux – several groups several
LynxOS – Lynx Real-Time Systems, Inc.
MacOS X Server – Apple Computer, Inc.
NetBSD – NetBSD Group
NonStop-UX – Compaq Computer Corporation
OpenBSD – OpenBSD Group
OpenLinux – Caldera Systems, Inc.
Openstep – Apple Computer, Inc.
Red Hat Linux – Red Hat Software, Inc.
Reliant Unix – Siemens AG
SCO Unix – The Santa Cruz Operation Inc.
Solaris – Sun Microsystems (now ORACLE)
SuSE – S.u.S.E., Inc.
UNICOS – Silicon Graphics, Inc.
UTS – UTS Global, LLC