Will Windows go open source? Now that Microsoft "isn't a software company" any more, it's possible that at least some parts will become open source in the future. See also: Windows 10 UK release date, features and price
Back in April, Microsoft's Mark Russinovich was questioned on the possibility of Windows becoming open source. His reply wasn't what the ChefCon audience was necessarily expecting: "It's definitely possible".
ChefCon is an open source focused conference, with Russinovich being the CTO of Azure, Microsoft's cloud computing platform. He also said that the company is "having every conversation that could be imagined about what to do with its software and services".
To understand what an open source Windows would mean, you need to understand the difference between closed source and open source. Put simply, Windows - like Mac OS X - is closed source. The code that runs these operating systems is not publically available. Open source software is purposefully made available for anyone to play with it, modify it and create their own version of the software.
Linux is a well-known open source OS and there are many versions - known as distributions - which various people and groups have developed. Android is based on Linux and is also open source, which is one of the reasons it's such a popular mobile OS.
There are many arguments for and against open source software, so moving Windows from closed- to open source isn't something Microsoft will treat lightly. Until now, keeping the source code secret has made the company a lot of money but with the shift from desktop PCs to mobile devices and the cloud (aka the 'Third Platform') Microsoft's new CEO really had no choice but to quickly change the company's focus to "mobile-first, cloud-first" rather than Windows software first.
This is why it makes sense to make at least parts of Windows open source. Having derided open source software in the past, Microsoft is in the process of a U-turn and in 2014 made the .Net framework open source. .Net was originally for developers to make Windows programs, but now they can use it for building apps on other OSes.
Evidence that selling Windows licences is no longer the priority, Microsoft is offering a free upgrade to Windows 10 for practically everyone when it launches later in 2015. Money will instead be made by - among other things - selling Office 365 subscriptions, OneDrive storage and other services to not only Windows users, but those on other platforms as well: Office is now available on iOS and Android as well as Windows Phone.
Making Windows open source would mean there could be a much higher contribution from software engineers to make the OS more secure. But the nay-sayers have the opposite opinion: open source software means more bugs and less security.
An open source Windows would also lead to multiple versions, just as you get with Linux. This creates confusion and could be a problem as Microsoft can't provide support for every version. Hence, it will be a long while before we hear any official announcement. Right now, Microsoft's official line is that it hasn't made any business model changes for Windows.