Matrix is also decentralized/federated, has encryption integrated into the protocol and enjoys a broad adoption and public support. It also has pretty good integration of bots and even other message protocol services like IRC via “bridges”. The chat clients are pretty good too; Element is pretty much available for every platform but there’s other one’s which are more focussed on Desktop or mobile usage, depending on how you primarily use it.
There’s an even better alternative on the CCC’s website, the original source of the video ;)
https://media.ccc.de/v/34c3-9064-the_ultimate_apollo_guidance_computer_talk