But there are a few things going on here.<p>1) All of .NET is open sourced under the Apache License (not some weird MS license)<p>2) Xamarin had started taking thousands of lines of code from the open sourced .NET framework and replacing parts of Mono with it (like System.Decimal, etc). So that merge had started happening anyway.<p>3) The &quot;Mono&quot; differentiation was probably going to go away with .NET Core maturing.<p>4) MS needs a quick step up with cross platform toolkits for .NET, and nobody better than Xamarin, who&#x27;s been doing it for a decade.<p>If they abandon Xamarin, you still have an APL&#x27;d .NET framework that&#x27;s fully developed out in the open, and nobody is really left in a lurch. You can fork it.