Mono is an open source implementation of Microsoft's .NET Framework that allows developers to build and run .NET applications on Linux, macOS, Windows and other operating systems. It supports many popular programming languages used in .NET development like C#, VB, F# and provides tools like MonoDevelop for building applications. Mono implements many of the core .NET APIs and frameworks and is compatible with Microsoft's .NET stack, making it possible to port existing .NET applications to other platforms. The Mono project is led by Xamarin and sees ongoing development to improve compatibility with .NET.