#threema
Threema is the world’s best-selling secure messenger and keeps your data out of the hands of hackers, corporations, and governments.

Each Threema user receives a random Threema ID for identification. A phone number or email address is not required to use Threema. This unique feature allows you to use Threema completely anonymously – no need to give up private information or to open an account.

To bypass The App Store (Apple) & Google Play (Android) you simply download the messenger directly from the Threema website.
https://shop.threema.ch/en