Signal has open source clients and server. Matrix has crypto support now (needs more auditing, but you can turn it on and nobody has cracked it yet to my knowledge) and thats fully open source.
No, open source does not guarantee they are using the secure algorithms advertised on their servers. But open source does is let you run your own server, that you can put much more trust in. People spin up their own signal and matrix servers all the time now for just that reason.
No, open source does not guarantee they are using the secure algorithms advertised on their servers. But open source does is let you run your own server, that you can put much more trust in. People spin up their own signal and matrix servers all the time now for just that reason.