Signal then SimpleX. SimpleX is really cool and new but you canβt have groups larger than 50 people. It was recently smeared by Wired as being a haven for neo Naziβs but thatβs bullshit unless you want to accuse Monero of being solely for illicit deeds and money laundering.
Also, thereβs Matrix which is like a federated Discord and NOSTR which is also being smeared but is a quite promising technology that Jack Dorsey was looking into and Edward Snowden uses.