Briar is really good. Not only can it route over actual Tor (the default!), it can also be distributed, installed, and even used _completely_ offline^1. I'm genuinely impressed by the ingenuity and flexibility of this little marvel of an app. My only complaints are that it doesn't support sending arbitrary files, it can't route via the normal internet, and the UX is a bit "off" (e.g. read checkmarks don't have the semantics of their whatsapp counterpart despite looking the same).
Whether it's natural disasters, wars, or just plain old internet , I bet many people will be extremely glad to know this app exists.
[1]: It gives you an option to start a local server to share the app via hotspot and maybe bluetooth (not sure about this one). Accounts are created locally and are completely decentralized. Messages can be routed via local networks, bluetooth, and/or even carrier pigeons (via usb/sd cards).
But good on her for sticking with her principles.
I did decide to use Session as a result of this bill, though, since that routes through a Tor-like system.