Mono is a project led by Novell (formerly by Ximian) to create an Ecma standard compliant .NET compatible set of tools, including among others a C# compiler and a Common Language Runtime. Mono can be run on Linux, BSD, UNIX, Mac OS X, Solaris and Windows operating systems.
Microsoft has a version of .NET available for FreeBSD, Windows and Mac OS X called the Shared Source CLI (Rotor). Microsoft’s shared source license may be insufficient for the needs of the community (it explicitly forbids commercial use). The Mono project has many …

ReactOS is a computer operating system intended to be binary-compatible with application software and device drivers made for Microsoft Windows NT versions 5.x and up (Windows 2000 and its successors). It is composed entirely of free software, by means of a complete clean room reverse engineering process.
Although the project is in the alpha development stage as of 2008, many Windows programs already work well. While the ReactOS kernel has been written from scratch, the userland is mostly based on the Wine compatibility layer for Unix-like operating systems.
ReactOS is primarily written …

QNX (pronounced either Q-N-X or Q-nix) is a commercial POSIX-compliant Unix-like real-time operating system, aimed primarily at the embedded systems market. As of September 12 2007, the source of the QNX kernel has been released for non-commercial use.

Description
As a microkernel-based OS, QNX is based on the idea of running most of the OS in the form of a number of small tasks, known as servers. This differs from the more traditional monolithic kernel, in which the operating system is a single very large program composed of a huge number of …

Wine is a software application which aims to allow Unix-like computer operating systems on the x86 architecture to execute programs that were originally written for Microsoft Windows. Wine also provides a software library known as Winelib which developers can compile Windows applications against in order to port them to Unix-like systems.
The name ‘Wine’ derives from the recursive acronym Wine Is Not an Emulator. While the name sometimes appears in the forms “WINE” and “wine”, the project developers have agreed to standardize on the form “Wine”.
The Wine developers released the first …

Xserve is the name of Apple Computer’s Macintosh 1U rackmount line of server computers.
While Apple’s first foray into the server market in 1997 was a spectacular failure by way of Network Servers that ran AIX 4, the introduction of OS X in 2000 and the later rollout of the G5 PowerPC processor from IBM present strong arguments for its adoption now.
Not known for being a server-side company, Apple representatives confirmed that the company took its efforts to penetrate the enterprise market very seriously and spoke to hundreds of companies during …