The bridges made for Beeper are all open source (https://github.com/mautrix/ https://github.com/mautrix/), so you can set up your own Matrix server with bridges

The bridges made for Beeper are all open source (https://github.com/mautrix/ https://github.com/mautrix/), so you can set up your own Matrix server with bridges and use any open source Matrix client (https://matrix.org/ecosystem/clients/ https://matrix.org/ecosystem/clients/). Besides Beeper, the only consumer bridge hosting service I'm aware of is Element One, but it's only barely maintained, so I'd definitely recommend self-hosting over that.