Mono Microsoft.CSharp library (for CLI 4.0) Mono is a platform for running and developing applications based on the ECMA/ISO Standards. Mono is an open source effort led by Novell. Mono provides a complete CLR (Common Language Runtime) including compiler and runtime, which can produce and execute CIL (Common Intermediate Language) bytecode (aka assemblies), and a class library. This package contains the Mono Microsoft.CSharp library version 4.0.