Doesn't exist yet. But with signal protocol being reimplemented in Rust (as libsignal-client), it should be possible soon.
It works (in principle), but uses deprecated swarm client. This "old Swarm network" was shut down on 2021-01-25.
It also requires a password to Ethereum key given in plaintext file.
Have fun with it, study how it's implemented, but don't try to use for anything serious.
Source code is available at: codeberg.org/etam/tigermail
Building from source is a huge PITA, due to aleth making it very hard to use its shared libraries separately.