I played with @delta and *damn* is it sweet!
It uses my e-mail account as transport, but encrypts using OpenPGP, and feels like IM. Has groups and all.
It's not exactly a @signalapp replacement (yet?): a). it obviously leaks metadata, as it uses e-mail as transport; and b), it uses Autocrypt for key exchange and I have not found a way to *pin* known keys for certain accounts.
But it's interesting! I will keep an eye on it; 
saga shows why we need to move away from walled gardens.
@rysiek Love it! Even does Jitsi video calling. My article about it was very popular last year. https://pocketnow.com/10-ways-delta-chat-is-better-than-whatsapp-signal-and-telegram/
@rysiek That kind of talk is over my head. :) But their contribution forums are really helpful and responsive with feature proposal ideas and such: https://support.delta.chat/
@adam good one!
I do think the biggest missing feature (unless it's there and I just missed it?) is the ability to *pin* the key for a contact and ignore Autocrypt for that contact from that point on.
If I understand Autocrypt correctly, it is not designed to protect from an active, MitM-capable attacker. Which makes it not an option in a lot of contexts.