Mono, the open source development platform based on the .NET framework, allows developers to build cross-platform applications with improved developer productivity. Mono’s .NET implementation is based on the ECMA standards for C# and the Common Language Infrastructure.
Sponsored by Novell, the Mono project has an active and enthusiastic contributing community. Mono includes both developer tools and the infrastructure needed to run .NET client and server applications. (http://www.mono-project.com/)
