Mono is a free and open source project led by Novell to create an Ecma standard compliant .NET-compatible set of tools including, among others, a C# compiler and a Common Language Runtime.

The stated purpose of Mono is not only to be able to run Microsoft .NET applications cross-platform, but also to bring better development tools to Linux developers. Mono can be run on Android, BSD, iOS, Linux, macOS, Windows, Solaris, and Unix operating systems as well as some game console operating systems such as the ones for the PlayStation 3, Wii, and Xbox 360.