Microsoft wants Outlook to be the one destination you have to visit to know what's going on. It also wants to make use of the talent it acquired when it purchased Sunrise. So the company is delivering on old promises by introducing Calendar Apps, which let you see tasks and notes from different sources. The opening salvo of supported services consists of Evernote, Facebook, and Wunderlist.
Evernote integration means being able to view notes or reminders directly on your calendar. An example would be designating when you're going shopping by making that block of time a list of what you need to get. Facebook integration shows you your friends' birthdays and the events you've agreed to attend. Wunderlist to-do items mark the time that they are due.
Evernote and Wunderlist also have add-ins available for Outlook.com. You can get details on those at the links below.