Oparating system Developers

* Microsoft
* Unix
* Sun
* Apple
* IBM
* Commodore
* BSD
* SCO
* Corel
* GNU
* Digital
* SGI
* Kondara
* Linus Trovalds
* Mandrake
* OSF
* QNX
* Red Hat
* Suse
* Bell Labs
* UnixWare


Microsoft Windows





* Microsoft Windows Vista (aka Windows NT 6.0) (codename: Longhorn)
* Windows Server 2003 (aka Windows NT 5.2)
* Microsoft Windows XP (aka Windows NT 5.1) (codename: Whistler)
* Microsoft Windows 2000 (aka Windows NT 5.0)
* Windows NT 4.0, 3.51, 3.5, 3.1
* Windows Me (aka Windows 4.9)
* Windows 98 SE (Second Edition) (aka Windows 4.2)
* Windows 98 (aka Windows 4.1)
* Windows 95 (aka Windows 4.0)




MacOS (Apple Macintosh)

* Mac OS X v10.5 (Leopard) (planned for release in late 2006/early 2007)
* Mac OS X v10.4 (Tiger)
* Mac OS X v10.3 (Panther)
* Mac OS X v10.2 (Jaguar)
* Mac OS X v10.1 (Puma)
* Mac OS X v10.0 (Cheetah)
* Mac OS 9
* Mac OS 8
* Mac OS 7.6 (first officially-named Mac OS)
* System 7 (code-named "Big Bang")
* System Software 6 and earlier



Linux is an Open Source Operating system





* Ubuntu
* Debian
* MEPIS
* openSUSE
* SUSE Enterprise Linux
* Fedora
* Red Hat Enterprise Linux
* CentOS
* Mandriva
* Xandros
* Linspire (previously known as "LindowsOS")
* Gentoo
* Slackware


BSD

* DragonFly BSD
* FreeBSD
* PC-BSD
* NetBSD
* OpenBSD


Solaris





* Nexenta
* Solaris


Other

Other operating systems currently in use, and appropriate for specifically targeted web applications and testing, but not considered to be in mainstream use.

* Inferno
* SkyOS
* Digital UNIX (aka Tru64)