OS X Server!

Gentoo Linux is a versatile, fast, highly configurable and completely free Linux and FreeBSD distribution geared towards developers and network professionals.

Red Hat is the leader in development, deployment, and management of Linux and open source solutions for Internet infrastructure - ranging from embedded devices to secure Web servers. Red Hat was founded in 1994 by visionary entrepreneurs Bob Young and Marc Ewing. Open source is the foundation of our business model. It represents a fundamental shift in how software is created. The code that makes up the software is available to anyone. Developers who use the software are free to improve the software. The result: rapid innovation. Red Hat solutions combine Red Hat Linux, developer and embedded technologies, training, management services, technical support. We deliver this open source innovation to our customers via an Internet platform called Red Hat Network. Red Hat is headquartered in Raleigh, North Carolina, USA. »

CoreOS is a new Linux distribution that has been rearchitected to provide features needed to run modern infrastructure stacks. The strategies and architectures that influence CoreOS allow companies like Google, Facebook and Twitter to run their services at scale with high resilience. We've implemented them correctly so you don't have to endure the slow, learn-as-you-go infrastructure building process.

ClearOS is a family of operating systems for the enterprise, small business, and home. There are three editions to choose from depending on your needs and suitable to your abilities. They are: ClearOS Enterprise, ClearOS Home, and ClearOS Core.

Zentyal is a native Microsoft Active Directory® implementation on Linux incorporating all the network services required in a small and medium business environment: Directory & Domain Server, Mail Server, Gateway and Infrastructure Server.

NethServer is a CentOS-based Linux distribution for servers. The product's main feature is a modular design which makes it simple to turn the distribution into a mail server and filter, web server, groupware, firewall, web filter, IPS/IDS or VPN server. It also includes a comprehensive web-based user interface that simplifies common administration tasks and enables single-click installation of several pre-configured modules. NethServer is designed primarily for small offices and medium-size enterprises. »

Univention Corporate Server is a pre-configured Linux server operating system free of charge. It's the best fit to provide Microsoft Server-like services on the cloud or on the premises, to run and operate corporate IT environments with Windows- and Linux-based clients and to extend those environments with proven enterprise software, also either on the cloud or on the premises.

IPFire is a server distribution with intended to use as a firewall. It focuses on flexibility, and scales from small to middle sized business networks and home networks.

Windows Server 2012, codenamed "Windows Server 8", is the sixth release of Windows Server. It is the server version of Windows 8 and succeeds Windows Server 2008 R2. Two pre-release versions, a developer preview and a beta version, were released during development. The software was generally available to customers starting on September 4, 2012.

The Amahi Home Server is designed for home and small office environments where the technical support staff do not want the job!

SUSE is the original provider of the enterprise Linux distribution and the most interoperable platform for mission-critical computing. It's the only Linux recommended by VMware, Microsoft and SAP. And it's supported on more hardware and software than any other enterprise Linux distribution

Superb Mini Server (SMS) is a Slackware-based server distribution with web, DNS, DHCP, file, print and fax servers, iptables firewall, mail server with spam filter and anti-virus scanner, and BitTorrent station. It also includes Webmin, a web-based administration tool, but no graphical desktop. SMS, which comes with Slackware's text-mode system installer, is built using Linux-Live scripts (from Slax) and can be used as a live CD for testing purposes.

Endian Firewall Community (EFW) is a "turn-key" linux security distribution that turns every system into a full featured security appliance with Unified Threat Management (UTM) functionality. The software has been designed with "usability in mind" and is very easy to install, use and manage, without losing its flexibility.