As its website describes it, Mono is a “cross platform, open source, .NET development framework.” .NET is a framework originally created by Microsoft, and the Mono developers from Novell created Mono to be interoperable with .NET applications. The result is .NET compatibility across Windows, Linux, and Mac OS X.
With Mono, developers can create C# and .NET applications that will work on almost any platform. What this means for server administrators is the ability to provide their services to various clientèle without having to make multiple versions of their applications. It is also a way to distribute their content even in virtualization environments.
Mono is free and open source software and is available for most Linux distributions, although its Novell origins mean that SUSE Linux Enterprise Server supports it out of the box. To install Mono on RHEL/CentOS/Fedora, simply open a terminal, login as root, and type:
# yum list mono*
You can then see which mono applications you want to install or install them all with:
# yum install mono*
Source: Mono Project