For those not in the know, Mono is a software platform designed to allow developers to easily create cross-platform applications.It is an open-source implementation of Microsoft's .NET Framework based on the ECMA standards for C# and the Common Language Runtime.

Wine already uses Mono, and this move makes sense with Microsoft focusing on open-source .NET and other efforts.

According to Phoronix's Michael Larabel, formally handing over control of the upstream Mono project to WineHQ is a nice move by Microsoft rather than just letting the upstream Mono die off or be forked.

Microsoft's Jeff Schwartz announced the move on the Mono website and in a GitHub post:

The Mono Project has been an important part of the .NET ecosystem since its launch in 2001. Microsoft became the steward of the Mono Project when it acquired Xamarin in 2016.

The last major release of the Mono Project was in July 2019, followed by minor patch releases until February 2024.

Source code in existing mono/mono and other repos will remain available, although repos may be archived. Binaries will remain available for up to four years.

Microsoft maintains a modern fork of Mono runtime in the dotnet/runtime repo and has been progressively moving workloads to that fork.

 That work is complete, and it recommends that active Mono users and maintainers of Mono-based app frameworks migrate to .NET, including work from this fork.

“We want to recognise that the Mono Project was the first .NET implementation on Android, iOS, Linux, and other operating systems. The Mono Project was a trailblazer for the .NET platform across many operating systems. It helped make cross-platform .NET a reality and enabled .NET in many new places and we appreciate the work of those who came before us,” a spokesVole said.