Xbox Ones friends list app has been shown in action in a new video posted by Microsoft. It shows how players can watch what their friends are up to in real-time.

Profiles viewed in the friends list app will reveal your uploaded videos, follows, achievements, rep and more. You can also tag friends as favourites for quick access later. You can also follow people without becoming their friend. Users can tweak their settings to ensure that followers cant just follow them at random. Its up to you if you want to block this feature.
You can have up to 1,000 friends on your list on Xbox One, and you can see their Xbox One and Xbox 360 activity at a glance.
There are also two types of achievements on Xbox One. Larry Major Nelson Hyrb wrote on his blog

There are now two types of Achievements: achievements and time-based challenges. The former is similar to the achievements you earn on Xbox 360. Challenges on the other hand are only available for a certain period of time. What you accomplish during that timeframe will count towards unlocking the challenge.
As a nod to our stellar community, many challenges require a community to work together towards a common goal. Imagine, for example, a game releases a weekend objective that requires players to cumulatively secure an objective X number of times in a three day period. And every person who participates and helps build towards the challenges goals unlocks that Achievement and earns its reward.

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