The protests in Hong Kong often use mesh apps for their communication, like #Briar.
Sorry, article in German. Crucial sentence:
"For communication and coordination, after negative experiences with Telegram and Line, so-called Mesh-Apps like Firechat or Briar are used, which operate without W-Lan and telephone network."
Unfortunately the project just ran out of money. So if you have something to spare, go for it.
Single user instance.