There's element call as well. (https://call.element.io)

I'm not sure that spreading salt is a good idea when you consider that salt kills life when you spread it on land.

Carnet on f droid.

There's actually a very good scifi story idea here

Matrix is searchable through https://archive.matrix.org/

Weird, when was that ? In onboarded 6 non-tech people recently on element and it went fine and easy.