It’s not p2p but at least many years ago:

SMS.

If the Internet outage is local then the towers would still work and you’d be able to get texts. I went through a few storms where wired home internet was down, the towers weren’t giving me a data connection (no mobile web browsing or anything), but I was able to send and receive texts.

If you really care about what you’re asking after, do what someone else said and get a radio license. It’s 150 year old technology and every time something happens radio operators pop up some kind of emergency communications or bridge to the internet through repeaters or something.

Briar or meshtastic

Depending on how far you're willing to push the definition of "messaging" you could look into getting your ham radio license. It can't possibly be censored and allows you to communicate all over the world. You can even build your own radios if a government cracks down on them for some reason.

The first thing that comes to mind is Meshtastic: https://meshtastic.org/

Briar (Android Only) - Uses Bluetooth, Wifi, or Internet via Tor to communicate. You can theretically create a large mesh group with enough users. Think of protests where the government shuts down the internet. Downside is, bluetooth range is 10 meters 😓.

Also: You can send encrypted text over SMS using Secure Space Encryptor (SSE) (known as Paranoia Text Encryption on iOS). It's an Open Source app that can encrypt text.

1. Type text
2. Copy the Ciphertext
3. Send and tell the recipient to use SSE fo decrypt.

You both have to share a password/passphrase over a secure channel, then use that to encrypt and decrypt.

Or PGP (there are mobile apps), but they aren't quantum resistant. If someone intercept and stores them, it could be decrypted later. So I recomment Symmetric Encryption like AES 256 (so use SSE for better security, since they use AES 256)

You can also encrypt a radio:

Rattlegram is an app on iOS/Android that alllows converting text to audio and play it over your phone’s speaker.

As mentioned before, SSE.

1. Use SSE to encrypt text
2. Copy-Paste the Ciphertext to Rattlegram
3. Sent it over the radio
4. On the other end, use Raddlegram to turn the audio back to the ciphertext
5. Use SSE to decrypt.

Voila! Off-Grid Encrypted communications.

Warning: Encryption over Ham Radio bands is illegal in many countries 😉 (but fuck the law lol, who cares)

There's also Meshtastic, but it has much shorter range, but, in the USA at least, they aren't "Ham Radio" so they (supposedly) can be encrypted legally.

This was a common thing that was developed for the international protests after Arab Spring, which would frequently have their Internet shut down as a State tactic to prevent communication amongst protestors.

Mesh net chat apps like FireChat were born in response

https://en.m.wikipedia.org/wiki/FireChat

Edit: apparently wikipedia says it wasn't developed for protests, it just happened to be released at the same time

https://adps-project.org/

Meshtastic can be encrypted and is LoRa based. Can easily hit nodes dozens of miles away with a good line of sight. It also relays messages across nodes to reach even further distances.

yggmail is a fairly obscure and experimental take on email on a mesh network: https://github.com/neilalexander/yggmail

I mean this is a terrible answer, but DS pictochat fits that

Yes, it's possible. To be honest, I find it very sad that we have grown so dependent on ISP and big telecom companies to have a working network.

In theory, you could have an infrastructure in your neighborhood and be able to play Quake with your neighbors without making use of the phone line at all, completely free of monthly fees and with a very efficient and fast connection too! you'd just need cabling connecting the apartments/houses and some decent routers controlling/restricting access on each subnet. It's a pity that's not a standard thing when designing residences.

Though less efficient and more limited in range, you can technically do it with Wifi and mesh networking too... there are projects like B.A.T.M.A.N (https://www.open-mesh.org/), however, it's not very user-friendly to set up. I believe there have been some projects that attempted to launch embedded devices to act as mini routers for this, but the spread has not been wide enough to make it worth it, sadly.

positive-intentions is a decentralised P2P chat app. https://positive-intentions.com/

Yea but there are android versions too. Its to send files over WiFi direct phone to phone with no network but some also have chat.

Surprised nobody mentioned scuttlebutt yet https://scuttlebutt.nz/

Briar has a mesh mode. And i think there was a matrix app doing this too?

Check out Reticulum Network Stack using LORA radio. Works really well.

http://reticulum.network/

Thereis stuff like

https://meshtastic.org/

https://unsigned.io/private-messaging-over-lora/

If you don't want to use internet the only ways are to use radio or deploy your own network infrastructure (optic fiber or cell tower), so there's no really any messaging app that can be used without internet. Briar can use Bluetooth but with a limited range, needing an actual dense mesh network.

Besides the already mentioned Briar, there's Berty, can't speak to its quality since I never used it, but I always found the project neat in and of itself

There used to be one years ago that used WiFi radios or Bluetooth or whatever so you could chat to people near you... I totally forget what it was called though.

yes, a lot of people were using those kinds of apps during the free hong kong protests, they go from device-to-device with no internet in between.

No idea what the app is called, but apps like those exist

This one works, if you don't mind a little diy and texting only: https://circuitmess.com/products/chatter-lora-communication-device

scratch telegram off that list, put Session messenger there instead.

Telegram isn't private, one guy has the master key to the whole thing

wouldn't a cheap walkie-talkie be more practical in that situation?

i remember using this app some time ago ☞ https://f-droid.org/packages/org.jsl.wfwt/

@Ju135 Briar over WiFi or Bluetooth.