Threema. The Secure Messenger promo code

Threema is a private messenger from Switzerland. You do not need a phone number or an email address to use it: each account is identified by a random Threema ID, so it can be used anonymously.

Messages, voice and video calls, group calls and files are end-to-end encrypted, and the servers are located in Switzerland. Besides chats you get voice messages, polls, location sharing and the option to edit or delete sent messages, plus a desktop app and a web client. The code is open source and regularly audited, and there are no ads or trackers. Threema is paid once rather than by subscription.