Back in 2011, Microsoft launched Roslyn, a project to expose its .NET Compiler as a series of services. Now that project has gone open source, alongside a move by Microsoft to group all its open source activities under a new banner: the .NET Foundation.
Microsoft announced the plans to open source Roslyn at its Build 2014 developer conference in San Francisco, and actually switched the status of the project from "private" to "public" on its CodePlex site during the Day 2 keynote. Roslyn includes compilers for C# and Visual Basic. (The code hasn't yet been added to Visual Studio itself.)
"We're taking the next step in open source, and we're announcing a new .NET Foundation as the umbrella for all these projects," executive VP cloud and enterprise Scott Guthrie said. The project incorporates a large number of existing code projects, as you can see in the screenshot above. Most use the Apache 2.0 licence.
Disclosure: Angus Kidman travelled to San Francisco as a guest of Microsoft.