Meshline

Meshline is a free, open source messenger that keeps working when the internet and cell service do not. Nearby iPhones pass end to end encrypted messages to each other over Bluetooth, so friends and family can stay in touch during outages, disasters, and crowded events.

No account and no sign up
Private 1:1 chats and small private groups
A public nearby chat for everyone in range
Messages hop through other phones to reach further

Meshline is based on the open source bitchat project. Source code: github.com/psulli007/meshline.