Session

Signal's encryption is beyond reproach, but it requires a phone number — an identifier that maps directly to a real identity. For most people that is fine, but in some situations — journalists and their sources, activists in high-risk regions — registration itself becoming exposure is the problem.

Session goes to the opposite extreme: registration asks for nothing. One tap generates a random Session ID, and that string is your entire identity. No phone number, no email, no username.

Two technical characteristics:

• Onion routing. Messages do not go straight to a server but pass through several relay nodes, each knowing only the previous and next hop. The node where a message lands does not learn your IP, a layer of protection centralized services like Signal cannot offer.
• A decentralized node network. Messages are held on distributed service nodes rather than one company's data center, so there is no single point whose shutdown takes the network down.

Add end-to-end encryption, disappearing messages, group chats and voice messages, and the everyday essentials are covered.

The trade-offs are real and must be stated:

• Adding contacts requires exchanging IDs out of band. No phone number means no contact matching, so that long ID string or a QR code has to reach the other person some other way. This is by design.
• Moving devices is awkward. No account means no login recovery, only a recovery phrase. Lose those words and both your identity and history are gone — write them down offline and store them safely.
• Speed and polish trail Signal. Multi-hop routing adds latency, delivery is less instant, and call quality is ordinary. That is the cost of the privacy, not a defect.
• The user base is small. Far fewer people use it than Signal, so you will usually be asking someone to install it specifically for you.
• It has had blockchain elements in its history. The project incorporated cryptocurrency-related design for node incentives, which some people dislike. Users need not touch any cryptocurrency, but if that background concerns you, read up before committing.

How to choose: everyday secure messaging → Signal, the best experience if a phone number is acceptable; hiding even that a conversation exists → SimpleX, the most thorough metadata protection; providing no identifier at all plus IP-layer protection → Session.

All three are open source and all three are cleaner than mainstream commercial messengers. Choose by your threat model.