The best alternatives to Zendo are Telegram Messenger, Signal 2.0, and Stealthy. If these 3 options don't work for you, we've listed a few more alternatives below.
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Stealthy messages are encrypted before leaving your phone for true end-to-end encryption. It is decentralized, meaning your data is not stored on any servers and your messages go directly to your friends--no middleman. Stealthy even features public channels for chatting with new people and the worlds first decentralized Ask Me Anything!
Threema is the world’s best-selling secure messenger and keeps your data out of the hands of hackers, corporations, and governments. Threema can be used completely anonymously, allows to make end-to-end encrypted voice and video calls, and offers every feature one would expect from a state-of-the-art instant messenger. With Threema Web, you can also use Threema from your Desktop.