Mono is an open source version of the .NET Framework developed by the community. It uses the exact same principles that Microsoft .NET Framework uses. It's compatible with the Microsoft .NET Framework. Even if you don't use ASP.NET 5, you can create assemblies on a Windows machine using the Microsoft .NET Framework and Visual Studio and run them on Mono on a Linux machine. So, an important difference with Microsoft .NET Framework is that it is cross-platform. Versions are available for Windows, macOS, and Linux. It's also used as the basis for Xamarin, which runs .NET on Android and iOS.