[8] Miguel de Icaza of Ximian believed that .NET had the potential to increase programmer productivity and began investigating whether a Linux version was feasible.

[9] 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.

[13][14] 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.

[15] 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.

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

[21] Some missing parts of the .NET Framework are under development in an experimental Mono subproject called Olive.

[22] The Mono project has also created a Visual Basic .NET compiler and a runtime designed for running VB.NET applications.

[26] According to Miguel, two factors sealed the fate of the project: Microsoft added "artificial restrictions" that "made it useless for desktop programming", and the technology had not gained enough traction on the Web.

[29] The Microsoft compatibility stack provides a pathway for porting Windows .NET applications to Linux.

As these components are not covered by Ecma standards, some of them remain subject to patent fears and concerns.

The Common Language Specification (CLS) is specified in chapter 6 of ECMA-335 and defines the interface to the CLI, such as conventions like the underlying types for Enum.

Other .NET or Mono applications can use legacy code, which is referred to as unmanaged, by using the System.Runtime.InteropServices libraries to create C# bindings.

Microsoft's shared source license may be insufficient for the needs of the community (it explicitly forbids commercial use).

MonoDevelop was originally a port of SharpDevelop to Gtk#, but it has since evolved to meet the needs of Mono developers.

The IDE includes class management, built-in help, code completion, Stetic (a GUI designer), project support, and an integrated debugger.

[47] Xamarin.iOS (previously named MonoTouch) is a library that allows developers to create C# and .NET based applications that run on the iPhone, iPod and iPad devices.

Unlike Mono applications, Xamarin.iOS "Apps" are compiled down to machine code targeted specifically at the Apple iPhone and iPad.

The Xamarin.iOS stack is made up of: Xamarin Studio is used as the primary IDE, however additional links to Xcode and the iOS simulator have been written.

From April to early September 2010, the future of MonoTouch was put in doubt as Apple introduced new terms for iPhone developers that apparently prohibits them from developing in languages other than C, C++ and Objective-C, and the use of a middle layer between the iOS platform and iPhone applications.

"[74] In August 2010, a Microsoft spokesman, Tom Hanrahan of Microsoft's Open Source Technology Centre, stated, in reference to the lawsuit filed by Oracle against Google over Android's use of Java, that "The type of action Oracle is taking against Google over Java is not going to happen.

[80] Mono is dual licensed by Xamarin, similar to other products such as Qt and the Mozilla Application Suite.

[87] Mono's implementation of those components of the .NET stack not submitted to the ECMA for standardization has been the source of patent violation concerns for much of the life of the project.

In June 2009 the Ubuntu Technical Board stated that it saw "no reason to exclude Mono or applications based upon it from the archive, or from the default installation set.

"[90] The Free Software Foundation's Richard Stallman has stated on June 2, 2009, that "[...] we should discourage people from writing programs in C#.

[92] Fedora Project Leader Paul Frields has stated, "We do have some serious concerns about Mono and we'll continue to look at it with our legal counsel to see what if any steps are needed on our part", yet "We haven't come to a legal conclusion that is pat enough for us to make the decision to take mono out".

Some programs written for the Linux Desktop include Banshee, Beagle, F-Spot, Gbrainy, Docky/GNOME Do, MonoTorrent, Pinta, and Tomboy.

The program, Logos 5 Bible Study Software (OS X Version), was written for the MacOS.

[95] OpenRA bundles its Apple Disk Image and Linux AppImages with Mono essentially removing almost all dependencies from the game.