Manyverse is an alpha Android app for Scuttlebutt, the off-grid social network. It needs a lot of work at this point. But, it’s an interesting model I hope gets some traction.
If you need a pub server, try: http://ssb.learningsocieties.org
There are others software efforts that are similar. Compare Manyverse to Riot.im, Keybase, Mastodon, the Safe Network, and others.