Peer-to-peer communications

These tools work best when set up before the shut down. Peer-to-peer communication happens between technology connections that don't require the internet, such as bluetooth or when different devices are connected to a common network router using their WiFi.

Briar

The Briar app runs on Android, and is open source. It uses enctrypted messaging, and was designed with human rights activists, journalists and activitsts in mind. It's also useful for anyone else to have a secure method of communication. It uses the internet when it's available, but can also connect to other devices using local wifi routers or bluetooth.

Jami

Jami is an interesting cross-platform app that's open source and privacy preserving. It tries to find the most direct path for sending data. Users who are on the same local network can communicate with Jami even if they are disconnected from the internet.

Bridgefy

Bridgefy is another messaging app for Android and iPhones, created to preserve communications during an internet shutdown or outage. You will need to have an internet connection to run the set-up, though the first time you turn it on. After that, it works usng bluetooth connections.

Note: The above two apps can use your mobile's battery a bit more highly than standard chat tools.

Silence

Including Silence here, as it doesn't need internet, though does need access to SMS or MMS networks. If that's working, though, you can have message encryption with other Silence App users. It uses the Signal encryption protocol, but unlike the Signal app, it doesnt' require the internet to work (though that means some of the other privacy features of Signal aren't included).