At the conference Disrupt SF 2018 in San Francisco, a startup from USA presented a secure messenger on the basis of the blockchain platform Blockstack.
A product called Stealthy allows you to not only communicate using encrypted messages, but can become a platform for decentralized applications. For enhanced security, encrypted messages are sent to the cloud provider.
The user can choose cloud hosting for storing messages. Then the receiver using the app Stealthy can decrypt the message.
The app is already available for IOS and Android, and in the future the creators plan to charge for the corporate version of the product. It is noteworthy that the logo resembles a Stealthy sign of the messenger Telegram.