Researchers from several institutes worldwide recently developed Quarks, a new, decentralized messaging network based on blockchain technology. Their proposed system could overcome the limitations of most commonly used messaging platforms, allowing users to retain control over their personal data and other information they share online.
Unlike Bitcoin this ledger is not open to the public, it only exists on the nodes containing group members.
And everything in the ledger is encrypted except the timestamp. So without a decryption key, you could tell when messages were sent but not who sent them.