Xamarin is a cross-platform development tool that’s built on Microsoft-sponsored technologies, here’s the announcement:

As part of this commitment I am pleased to announce today that Microsoft has signed an agreement to acquire Xamarin, a leading platform provider for mobile app development.

In conjunction with Visual Studio, Xamarin provides a rich mobile development offering that enables developers to build mobile apps using C# and deliver fully native mobile app experiences to all major devices – including iOS, Android, and Windows.

This is a massive power grab from Microsoft, and could be leveraged to put them back on top. Consider that Microsoft have a way for developers to take iOS and Android codebases and ship it on Windows 10 using a compatibility-layer approach. If you look at their offerings on competitor’s platforms, you might think they’ve taken a “if you can’t beat them join them” approach, but it’s becoming more and more “if you can’t beat them become them.”