My advice would be Xmpp with OMEMO encryption. On mobile, you can get the Conversations App for Android via Fdroid (no google play!), for the iPhone there is Chatsecure and on the Desktop you can use Gajim.
The advantage over Signal would be that 1.) you don't have to share your telephone number and 2.) you don't rely on a single service provider/accounts are decentralized (there are various services for free and paid accounts and you could also host your own server)
e: Dear stranger, I'd be very interested in an explanation for your downvote. thanks!
The advantage over Signal would be that 1.) you don't have to share your telephone number and 2.) you don't rely on a single service provider/accounts are decentralized (there are various services for free and paid accounts and you could also host your own server)
e: Dear stranger, I'd be very interested in an explanation for your downvote. thanks!