technically nothing but it serves as a privacy respecting alternative to meta/google controlled messengers.

things like mastodon and pixelfed are rather easy to wrap your head around and replace their big tech counterparts with if you are the average user.

there is no real replacement for an instant messaging/sms like experience. matrix is at the moment still a bit too complicated to get into if you have come to expect a workflow like: download an app -> write your phone contacts a message.

so although it is not federated it is the best we have got at the moment in my opinion