Threema is a secure, privacy-focused messenger that offers end-to-end encryption for messages, voice, video, and group calls. It is designed to minimize data stored on servers and is fully GDPR compliant. The app supports anonymous use and is open source in parts, using the NaCl cryptography library for encryption.

Threema is the world's best-selling secure messenger that keeps your data out of the hands of hackers, corporations, and governments. It offers end-to-end encryption for messages, voice and video calls, group chats, and files. The app can be used anonymously without phone numbers or emails, and is fully compliant with GDPR. Servers are located in Switzerland.