Serverschool
Although many debates about which operating system is best for hosting a server usually revolve around linux and windows, they are just two of many server-ready
http://www.serverschool.com/dedicated-servers/popular-server-operating-systems
Freebsd
The freebsd project
http://www.freebsd.org
Osdata
A technical answer to the question: how does rhapsody stack up as a server operating system?
http://www.osdata.com
Wisegeek
A server operating system is a software developed to serve as a platform for running networked applications. most server operating...
http://www.wisegeek.com/what-is-a-server-operating-system.htm
Ictivity
Servers zijn het hart van uw ict-infrastructuur. u wilt over een optimaal server operating system (server os) beschikken? neem contact op met onze os experts
http://www.ictivity.nl/producten-services/ict-consultancy/ict-diensten/client-server-oplossingen/server-operating-system-os
Ubuntu
Ubuntu
http://www.ubuntu.com/business/server/overview
MS Windows
Find information about windows servers and other microsoft server applications, including windows server 2003, sql server, exchange server, and more.
http://www.microsoft.com/servers/
HP Nonstop
When service levels are paramount, customers can trust hp integrity nonstop servers for their most critical business applications. hp nonstop integrity computing offers enterprise customers and partners unstoppable availability and scalability, an open application development environment, java-based tools, and support for just about any standard on the market.
http://h20223.www2.hp.com/nonstopcomputing/cache/76385-0-0-0-121.aspx
Pcworld
Pcworld
http://www.pcworld.idg.com.au/article/151491/server_operating_systems
ZOS (IBM)
Your portal to z/os information. learn the latest about z/os, the highly secure, scalable, high-performance enterprise operating system. find links to downloadable z/os technology and migration to z/os.
http://www-1.ibm.com/servers/eserver/zseries/zos/