At the Mobile World Congress event in Barcelona, Microsoft offered a session titled "First look at the Windows 10 Universal App Platform." The company explained that its new Universal App Platform (UAP) is a superset of the WinRT runtime for Windows 8. It also offered a list of steps for converting universal Windows 8.1 apps into universal Windows 10 apps.
The presenters added that universal apps won't look exactly the same on all devices and that developers will be able to target their apps to particular device types.
In addition, Microsoft announced a new category of "hosted web apps" that will be available through the Windows store.