The Mono Project is a cross-platform, open-source .NET framework that allows developers to easily create applications across various operating systems. Originally launched in 2001, Microsoft took over as the steward of the project in 2016. The last major release was in July 2019, with the most recent patch release in February 2024. WineHQ will now be taking over as the stewards of the Mono Project. Microsoft maintains a modern fork of the Mono runtime in the dotnet/runtime repo, and suggests that users migrate to .NET. The Mono Project was a pioneer in bringing .NET to different operating systems, making cross-platform development a reality.
https://www.mono-project.com/