TLDR: Is there an Android app that would allow for reliable instant messaging in areas without internet of any sort?
I am looking for a free Android app that would allow several users to communicate with each other over short distances even when there may not be any internet connection available to them. This means that the app should be able to run in the background, connect to a mesh network of all other devices running the same app and send and receive messages reliably. Having to give the app special permissions is not a problem. (Though the previous option is preferable, if there is a way that works using a private WiFi (without it having to be connected to the internet) and a server hosted on a local machine I am also interested in it.)
I know this is asking quite a lot, however, a number of apps on Google Play claim to possess all these features. I have tried some of these that work via Bluetooth and ad-hoc WiFi but I found that none of them worked reliably. These include:
- FireChat: I know it used to work in the past but the current version does not
- Bridgefy: only seems to support text messages in the current version and is unreliable, but it's still the best I could find
- Briar: did not work well
- Signal: did not work well
- goTenna: likely works well but very expensive
I only tested these between two devices each time, might any of these work better in practice with more users as mesh networks should in theory? Is there an app that might help I have not tried yet? Or is there a point to trying out old versions of FireChat hoping to stumble upon a working one? If so, would I be able to trust it (both the APK from a mirror and the app data security-wise)?