prefer Signal

Signal will force you into using an Android or iOS mobile device—no alternatives—and you couldn’t have 2 Android devices (like a tablet, e-reader). You are forced to have a SIM card which gives away part of your identity. Servers are centralized & closed-source (closed for 2 years, rewritten history)—so did the NSA force in a backdoor? …We may never know. On Android, by default notifications are sent thru Google Service’s Firebase (fork Molly supports UnifiedPush now tho). The ToS is questionable with “don’t break the law” language.

Your ideal chat would be free software, P2P or federated+self-hostable servers, E2EE, & the only required personal info you share is your account ID (no phone or email).

You’d think Matrix fits the bill, but its high system requirements (especially storage) & majority Matrix.org mean defacto centralization around an org that controls the spec, the largest server, reference server, & most popular client.

What you are looking for is good ol’ XMPP with OMEMO or PGP set to required in all clients. Its server options run on a toaster, has years of smart engineering & open governance guiding the project, & being extensible by nature, means it’s not purely limited to chat/conferencing. XMPP appears to be the common chat option on the dark web for a reason. You can use gateways to puppet accounts on these untrustworthy networks too (such as messlidger to puppet Facebook Messenger is needed, but also Signal, Telegram, etc.).

Alternatively, Briar & its ilk are gotos, but P2P has some downsides (brains your battery hard on Android).