A free program for Android, by Entangle Messenger.
Entangle is the world’s first open-source, post-quantum, securely encrypted messenger. With its intuitive, modern design, it is a complete redesign of the mobile messenger experience. It combines the best elements of both worlds – a modern, intuitive interface and the security of encryption.
In addition to a clean and modern design, Entangle is built on top of a secure, open-source platform. This means that the entire platform is available to everyone, and there are no fees to use it. The developers of the app are also in the process of creating a free and open source version for desktop computers.