Moonlight is a discontinued free and open source implementation for Linux and other Unix-based operating systems of the Microsoft Silverlight application framework, developed and then abandoned by the Mono Project.

[3][4] Like Silverlight, Moonlight was a web application framework which provided capabilities similar to those of Adobe Flash, integrating multimedia, graphics, animations and interactivity into a single runtime environment.

In an interview in the beginning of June 2007, Miguel de Icaza said the Mono team expected to offer a "feasibility 'alpha' demo" in mid-June 2007, with support for Mozilla Firefox on Linux by the end of the year.

[9] After a 21-day hacking spree by the Mono team (including Chris Toshok, Larry Ewing and Jeffrey Stedfast among others), a public demo was shown at Microsoft ReMIX conference in Paris, France on June 21, 2007.

He explained that Microsoft had "cut the air supply" to it by omitting cross-platform components, making it a web-only plugin, and including Windows-only features.

[25] MoonBase is an experimental set of helper classes built on top of Moonlight.Gtk that can be used to create full blown C# desktop applications using the Moonlight (Silverlight 4.0) widgets and XAML files.

[28] Support included giving exclusive access to Novell for the following Silverlight artifacts:[29] Microsoft released two public covenants not to sue for the infringement of its patents when using Moonlight.

[34] The version of Moonlight that was going to be available direct from Novell would have access to licensed closed source media codecs provided free of charge by Microsoft.