AFAIK, nope. There are several personal projects which modify Signal to work on private infrastructure rather than use signal’s centralized service, but nothing intended for public consumption or at least not that I’ve heard of. Maybe search it.
Signal is good enough and has been pushing for more mainstream appeal and polish (e.g. gif search) Its Achilles heel and main drawbacks stem from it’s centralization: needing a phone number and routing thru Signal’s infra. But that can also benefits them in some ways. Most devs who would be tempted to change that would rather spend their time elsewhere: tox, matrix, i2p, tor, xmpp and irc shenanigans, etc. Signal is just hydrated, in its lane, unbothered; chugging along as its LLC dictates. No alarms, no fires, no compelling reason to do a hard fork.
Edit: it completely slipped my mind that Molly existed. So yeah there’s that. But they still use signal’s infra.
I’ve been been deepdiving the cryptcom privacy space over the last week, refreshing my knowledge that was last updated about a decade ago. Signal spooks me because of the number requirement and centralization, but the tech is fine. Matrix is the new hotness but the clients kind of suck. I wonder if there are any i2p based apps? But Signal (or in my case, Molly-FOSS) seems to be fine for most purposes. Unless you’re the secretary of defense… There’s always Tox if you don’t mind the fact that it’s in dev and unaudited.