Signal

Cannot access message content or call audio by design; stores only the minimum technical metadata required to route messages; contact discovery uses cryptographic hashing so the server never learns your address book — the collection architecture is genuinely exceptional for a consumer messaging app.

Never sells, rents, or monetises data — stated without qualification as a permanent commitment in the Terms of Service; third-party providers are used only for SMS verification; law enforcement gets almost nothing because almost nothing is retained.

Open-source clients allow independent verification of all encryption claims; nonprofit structure eliminates commercial data incentives; the Signal Protocol is the industry standard for E2E encryption — but US jurisdiction applies, the policy's age raises currency questions, and no security certifications are named.