For years, Microsoft has flirted with the open-source movement, trying to build bridges with developers that favor publicly released code over proprietary software. This week, the software giant finally made the big moves skeptics of its commitment to open source have been looking for.

At a keynote presentation at the Build developers conference in San Francisco Thursday, Microsoft executive Scott Guthrie announced the creation of the .Net Foundation, an organization that will take over stewardship of the important software framework.

Microsoft created .Net years ago for two reasons: to help developers write software for multiple versions of Windows, and to answer the rise of the Java programming language. But its Windows-centric framework hobbled its adoption.

The move is notable because former Microsoft CEO Steve Ballmer once called open source a “cancer.” Ballmer is no longer CEO, and his successor, Satya Nadella, is committed to changing Microsoft’s image in a number of ways—particularly by repairing relationships with developers.

.Net also lives close to the heart of Windows, which Microsoft has kept as its own proprietary software. While it’s not as dramatic a move as open-sourcing Windows, it will do. 

See also: Ballmer’s Microsoft: All MBA, No Developer Soul

Microsoft also announced Thursday it would release Roslyn, a set of .Net coding tools, as open source. And on Wednesday, Microsoft released the code behind WinJS, a set of libraries for writing Windows applications in JavaScript, the popular programming language favored by many Web and mobile developers.

Opening Up To Developers

These are not sudden moves. Microsoft Azure, the company’s collection of cloud services, already support Linux and other open-source software. And Microsoft’s Codeplex site hosts 28,000 open-source projects.

The moves are somewhat self-serving. At the very least, developers that embrace these technologies are better set up to write apps for Windows and Windows Phone, as well as for other platforms. But open source seems to be the price of entry for any software development platform that seeks wide adoption these days.

It is also a critical way in which nontraditional developers, without the resources and training professional software programmers enjoy, learn how to code—by studying publicly released source code. And in that way, too, Microsoft may get more app creators outside its business-software stronghold to consider its offerings.

Microsoft’s release of .Net, Roslyn, and WinJS may not sway hardcore open-source advocates still smarting over Ballmer’s 13-year-old remarks. But taken together, they seem proof enough that Microsoft is turning over a new leaf.

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