This app was mentioned in 3 comments, with an average of 2.33 upvotes
Just FYI, if you don't have internet access, which you quite often won't in natrual disasters or social unrest, Snapchat and all the rest of the proprietary centralized apps are not going to help anyone. If you do have wifi routers and a lot of other phones around you, then decentralized things like Rumble should work. You should have Rumble and a flashlight app on your phone. Always.
https://github.com/Marlinski/Rumble
If you don't always whisper then use this app to text each other via bluetooth.
Guys, check out Rumble.