BeReal is a social app built around one spontaneous post per day. Each user gets a two-minute window to share what they are doing.

Daily notification - One alert each day opens a two-minute posting window for everyone at once.
Front-back photos - Each post captures the scene and the person with both cameras at the same time.
No filters or uploads - Posts cannot be staged, filtered, or uploaded from the camera roll.
Friends feed - Posts are shared with friends to show daily life as it happens.

It is used by people who want a small daily exchange with friends instead of a polished public feed.