Currently I explore the Visual Studio 2015 RC and realized that Xamarin Studio is integrated into Visual Studio and its installer. My Question is: Is Xamarin from now on free in
If you go to the visualstudio.com Visual Studio 2015 RC cross-platform and mobile apps page, then read and scroll to the bottom, it appears that Microsoft is including Xamarin, and upon installing it you do have, as James said, the Xamarin Starter edition. In 2015 RC go to Tools, Xamarin Account to see your Xamarin license. I do not know the limitations, or any expiration date, of this Starter Xamarin Account.
Still, I don't know about you, but the Visual Studio 2015 RC "Community" edition I installed expires in less than 180 days. (Check the Help menu, go to "About...", and click on your license status to check.)
Let's say Xamarin Starter edition is free, but Visual Studio 2015 "Community" has an expiration date. So the bigger question might be whether Visual Studio 2015 "Community" will be free.
Without Xamarin though, Microsoft is offering C++ tools for cross-platform development, but scroll down to the bottom of the page and you might be surprised or confused at the download link description.