Official site; Commercially sponsored Debian-derived Linux distribution that focuses on usability, a regular 6-month release cycle, and a commitment to at least 18 months of security updates for every release.
http://www.ubuntu.com/
Multiplatform Ultra-Secure Operating System. Focus: portability, standardization, correctness, security, and cryptography.
http://www.openbsd.org/
FreeBSD information. Descriptions, downloads, documents, community, developer resources, support.
http://www.freebsd.org/
Linux OS by Novell. SUSE Linux Enterprise is the premier Linux operating system for the enterprise.
http://www.novell.com/linux/
Red Hat is the world's leading open source technology solutions provider with offerings including Red Hat Enterprise Linux, open source applications, security and systems management, virtualization, Services Oriented Architecture (SOA) solutions, server a
http://www.redhat.com/
NetBSD is a free multi-platform operating system based on 4.4BSD Lite.
http://www.netbsd.org/
Unix clone that is free, small, flexible, secure, and self-healing, leading to high reliability, even during software faults. Descriptions, FAQ, book, newsgroup, screenshots, bug reports, downloads.
http://www.minix3.org/
IBM home page for AIX; many IBM AIX resources, product and service descriptions, links.
http://www-1.ibm.com/servers/aix/
Distribution, products, and services for large scale, to small scale and web businesses. Strong in Asia Pacific region, largest Asian distribution, founded 1992. Sites in English, Chinese, Japanese.
http://www.turbolinux.com/
Develops, supports small/mid scale Unix server OSs and business system software for network computing; products, related services: OpenServer, OpenUnix, UnixWare. Unix intellectual property licensing. Was Santa Cruz Operation, Caldera Systems, Caldera Int
http://www.sco.com/