On Day Two of Build 2016, Microsoft made the announcement that developers have been hoping for since the company acquired Xamarin in February: Xamarin tools will now be free for all Visual Studio users.

Subscribers to both paid and free tiers of Visual Studio will have access, which lowers considerably the cost of developing native apps for iOS and Android in C# using Xamarin.

Microsoft also said it will soon open-source Xamarin SDKs for Android, iOS and Mac. “This includes native API-bindings and the basic command-line tools necessary to develop mobile apps,” Xamarin’s Nat Friedman further explained in a blog post. “It also includes our popular cross-platform native UI toolkit, Xamarin.Forms.”

That’s not the only new toy developers have to play with as of this week. Microsoft also released the first public preview of Visual Studio 15 at Build. The latest version of Visual Studio includes new style analyzers for C# and Visual Basic, a preview of a new JavaScript language service, and an ‘Open Folder’ feature that allows developers to navigate code bases without setting up projects and solutions.

There’s also a faster, lightweight install option. Microsoft cautions not to install VS 15 on your production environment, as it’s unsupported.

Finally, Microsoft is adding an Insider Program to the Dev Center in Windows Store. As in the Windows 10 Insider program, Insiders will be able to test and give feedback on new Dev Center features as they are created.

Developers with apps in the store can now further monetize their apps with affiliate ads, use A/B testing to measure customer engagement, more easily solicit feedback from users. A new Dev Center UWP app will allow developers to easily monitor a range of information about their app’s performance.