Neither Microsoft nor Miguel de Icaza, Xamarin's cofounder, are commenting on the rumors. De Icaza did tweet a couple of related tidbits on March 17, however:
"Working together with Microsoft's .NET team for the last four months has been an absolute delight. So excited about the future," de Icaza tweeted last night.
In November, Microsoft and Xamarin announced a tighter development and marketing partnership aimed at developers interested in writing apps in C# for iOS and Android devices. Xamarin CEO Nat Friedman said the two had stepped up their involvement in the months preceding the November 2013 announcement.
When asked by "Mr. 64" on Twitter if he had moved to Redmond or was working remotely for Microsoft, de Icaza tweeted:
"We collaborate over email; but we are an independent company, I don't work for MS."
Xamarin's founders have been members of Microsoft's Visual Studio Industry Partner (VSIP) program since Friedman and de Icaza were at Novell. Microsoft removed restrictions four or five years ago that prevented VSIP partners from extending Visual Studio for non-Microsoft platforms. As a result, Xamarin was free to build the Xamarin.iOS for Visual Studio product that is the cornerstone of today's Xamarin 2.0 platform
This year at its Build conference, Microsoft is expected to continue in that vein. Word has leaked that Microsoft is building a new version of Windows Presentation Foundation (WPF), the framework for building desktop applications, that many believed Microsoft had abandoned the way it had Silverlight. It sounds like the new WPF could be one of the topics addressed at Build. (De Icaza told another person on Twitter yesterday that he'd recommend using WPF to build new projects.)
Microsoft officials have been forging a number of partnerships with tool and framework vendors to try to grow the number of Windows 8 and Windows Phone 8 apps. Microsoft has struck deals with Unity, Havok, Marmalade and Corona Labs to help bring more games to its platforms. I don't know if it's indicative of Microsoft's planned approach with Xamarin, but the Softies do seem more intent on partnering with tooling and framework vendors than buying them outright.
Fun fact for Microsoft history buffs: This isn't the first time there have been rumors that Microsoft was interested in having de Icaza join the firm. Back in 2003, Microsoft Distinguished Engineer Don Box serenaded de Icaza to the tune of "Michele" during a rooftop party at PDC. (I was there!) Sadly, I think the video clip of this is gone. Update: Nope, the video lives on. You can download it from here. (Thanks Felix.)
One more fun fact: Microsoft is holding a press event on March 27 that is focusing on mobile and cloud. Office on iPad is likely the main announcement, but maybe a Xamarin purchase/investment could be part of this, too? (Just pure speculation and dot-connecting on my part about this piece.)