Our premiere mix network client, catshadow is a work-in-progress:

Catshadow provides mutual location hiding properties between communication partners. Clients make use of the PANDA (Phrase Automated Nym Discovery Authentication) protocol for exchanging spool identities and the Signal Double Ratchet keys. That is, this messaging system creates bidirectional metadata leakage resistant communications channels which are composed with two unidirection channels. Each unidirectional channel contains the required information to write to a correspondant’s remote message spool.