Closest I can think of would be Session. Runs on a decentralized onion routing network, end-to-end encrypted and anonymous.

Problem is that it's quite slow at times and a lot of maxis would have an aneurysm over how the onion routing nodes are secured by staking OXEN (soon to be Session Token), but the average user doesn't have to even think about that and it helps prevent sybil attacks like Tor is vulnerable to.

Still, I'd be interested in seeing what the Nostr devs could come up with!