Mono (software)

Mono is a free and open-source software framework that aims to run software made for the .NET Framework on Linux and other OSes. Originally by Ximian which was acquired by Novell, it was later developed by Xamarin which was acquired by Microsoft. In August 2024, Microsoft transferred ownership of Mono to WineHQ.

When Microsoft first announced their .NET Framework in June 2000 it was described as "a new platform based on Internet standards", and in December of that year the underlying Common Language Infrastructure was published as an open standard, "ECMA-335", opening up the potential for independent implementations. Miguel de Icaza of Ximian believed that .NET had the potential to increase programmer productivity and began investigating whether a Linux version was feasible. Recognizing that their small team could not expect to build and support a full product, they launched the Mono open-source project, on July 19, 2001, at the O'Reilly conference.

After three years of development, Mono 1.0 was released on June 30, 2004. Mono evolved from its initial focus of a developer platform for Linux desktop applications to supporting a wide range of architectures and operating systems - including embedded systems.

Novell acquired Ximian in 2003. After Novell was acquired by Attachmate in April 2011, Attachmate announced hundreds of layoffs for the Novell workforce, putting in question the future of Mono.

On May 16, 2011, Miguel de Icaza announced in his blog that Mono would continue to be supported by Xamarin, a company he founded after being laid off from Novell. The original Mono team had also moved to the new company. Xamarin planned to keep working on Mono and had planned to rewrite the proprietary .NET stacks for iOS and Android from scratch, because Novell still owned MonoTouch and Mono for Android at the time. After this announcement, the future of the project was questioned, MonoTouch and Mono for Android being in direct competition with the existing commercial offerings now owned by Attachmate, and considering that the Xamarin team would have difficulties proving that they did not use technologies they formerly developed when they were employed by Novell for the same work. However, in July 2011, Novell, now a subsidiary of Attachmate, and Xamarin, announced that it granted a perpetual license to Xamarin for Mono, MonoTouch and Mono for Android, which officially took stewardship of the project.

On February 24, 2016, Microsoft announced it had signed a definitive agreement to acquire Xamarin.

On August 27, 2024, Microsoft transferred ownership of Mono to WineHQ, the developer team of Wine, a Windows compatibility layer.

Mono's current version is 6.12.0 (as of June 2024^[update]). This version provides the core API of the .NET Framework and support for Visual Basic.NET and C# 7.0. LINQ to Objects, XML, and SQL are part of the distribution. Windows Forms 2.0 is also supported, but not actively developed, and as such its support on Mono is incomplete. Version 4.0 was the first version that incorporates Microsoft original source code that was released by Microsoft as part of the .NET Core project.