It will be available for free upgrade for all Windows 7 and 8.x users,
and will run all desktops/laptops/tablets, phones, mobile and IoT devices, as small as $35 Raspberry Pi. All those platforms will run same universal apps, from Windows 10 store.
On top of this, there is now a way to run web apps as Windows apps from Windows Store,
to install and run "classic" Win32 and .NET apps in secure "containers" on Windows 10,
to run Android Java/C++ Apps on Windows 10,
as well as to compile and iOS Objective-C Apps in Visual Studio and install and run on Windows 10!
Day One Keynote Presentation | Build 2015 | Channel 9
Huge news: Windows 10 can run reworked Android and iOS apps | The Verge
Microsoft brings Android, iOS apps to Windows 10 | Ars Technica
Welcoming Developers to Windows 10
Why Microsoft's Strategy For iOS And Android Apps Is Genius (And Insidious) - ARC - ARC
Microsoft Build 2015: Porting of Android and iOS apps to be simplified on Windows 10 - Tech2
Microsoft says developers can port iOS and Android apps to Windows 10 | Computerworld
Download Windows 10 Insider Preview ISO - Microsoft Windows