[cykros]

Keep an eye on Whitenoise. It's basically taken the technology behind Signal and placed it atop Nostr, so rather than signing up with a phone number, you do it with an npub (pubkey). Still in very early days so the features aren't all there yet, and battery use could be better, but they've got the basics of it working already.

[aaravchen]

SimpleX is another option. These don't have discoverability for lay people users just joining though, which is actually a huge network effect positive for Signal in the family and friends use cases. However it avoids the issues with the public group chat privacy. It ends up coming down to client and protocol features for those. SimpleX has a more extreme privacy threat model than Whitenoise so user contacts tend to be throw away (for good or bad), which generally doesn't work for public communities.

The real kicker is that almost nothing has the community automation tools and administration of Discord which is the really hard lift.