I don’t know why this gets downvoted. Xmpp is my solution as well. Lightweight, selfhostable and federated, it’s just a great solution. Briar is good as well and probably one of the best dungeo solution if your are an activist/journalist. But it wilk eat your battery as all p2p solutions will. Is you host your own xmpp server at home, that’s really as secure as it will get imho.