If you’d rather not pay the Beeper Cloud service is free and all of the matrix bridges it uses are open source.
The source code behind how Beeper Mini works is available as well but will require a client of some sort to be written since you can’t just use a matrix bridge and a matrix app.
The guy who started Beeper also created the Pebble Watch and they have always maintained open source alternatives for their bridges.
I’m just happy that a company with those ethics is the one to take up this fight against Apple, this could have been a $10/month app from a company who believes in closed source and pushing ads/tracking users’ data.
Beeper is a good company that actually cares about privacy and security and that should be commended.