Windows Calendar
Sidebar Geek provides some details on Windows Calendar:
Screenshot: Windows Calendar Main Window with Apppointments
Screenshot: Subscribing to Published Calendar
Screenshot: Publishing a Calendar to the Web
In Build 5270, you can see that Microsoft has chosen to use the same UI seen in Windows Photo Gallery and Windows Media Player. This makes sense, of course, as Microsoft wants to have consistency with their windows applications. The features within this build don't seem to have changed much from the previous build. You can add appointments, make them reoccuring, add new calendars, add new tasks - pretty much all the tasks you need for a calendar program. You can publish your calendars to the web and subscribe to new calendars that have been published by other users.
Source: Sidebar Geek