Mono is a magical sauce, mixed into the Unity recipe, which gives it a lot of its cross-platform capability. Mono is an open source project that built its own platform of libraries based on the API, specifications, and tools from Microsoft's .NET Framework. Essentially, it is an open source recreation of the .NET Library, was accomplished with little-to-no access to the original source code, and is fully compatible with the original library from Microsoft.
The goal of the Mono project is to provide cross-platform development through a framework that allows code, written in a common programming language, to run against many different hardware platforms, including Linux, MacOS, Windows, ARM, PowerPC, and more. Mono even supports ...