Hmmm... did anyone ever think about making a sort of local bulletin board system with a small computer/old phone/sbc? The machine provides a wifi hot spot, but when logged on people only have access to a single local website where they can post messages to one another.
One could even have messages carried between multiple of these systems #sneakernet style. Kind of an alternet.
stupid idea: bluetooth #sneakernet without internet connections. clients reside on the phone or computer of participants, and peer automatically with one another when close by (or maybe with a public access point), exchanging messages and propagating messages further with every contact. private and public messages can be read via a simple app
which actually sounds like something someone somewhere might already have created.