https://www.beeper.com/

It's an app to aggregate your chats over a encrypted Matrix protocol, but using Beeper's Matrix servers as relays.

There are complaints about the app being closed source, the app being incompatible with other matrix servers besides their own and they will be implementing an optional paid subscription in the future. All valid criticisms, but they also have released the source for the bridges to each service so that tech savvy people can set up their own service using a different Matrix app.

It's useful for me as an easy way to stay connected with the various contacts on those platforms (until Beeper I was prepared to just go radio silent on them), while still maintaining a degree of separation with Facebook.