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Zalo vs Signal: catalog facts
Zalo	Signal
Free Free to download and use for messaging and calls.	Free Free; developed by a nonprofit funded by grants and donations
Windows, macOS, Android, iOS	Android, iOS, Windows, macOS, Linux
Widely used in Vietnam, so most contacts there already have it Messaging and calling in one app	End-to-end encryption on every message and call using the open source Signal Protocol No ads, affiliate marketers or tracking
Official site is mostly in Vietnamese Closed source, run on the developer's servers	Requires a phone number that can receive an SMS or phone call to register Desktop app requires Signal to be installed on a phone first
Downloadable app, Hosted service	Downloadable app
Closed source	Open source
License not stated	License: AGPL-3.0
Not stated if an account is needed	Account needed
Not stated if it works offline	Needs internet
Official website Full listing and sources Checked September 24, 2026	Official website Full listing and sources Checked September 20, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.