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Signal vs Viber: catalog facts
Signal	Viber
Free Free; developed by a nonprofit funded by grants and donations	Free Free to download and use for messages and calls.
Android, iOS, Windows, macOS, Linux	Android
End-to-end encryption on every message and call using the open source Signal Protocol No ads, affiliate marketers or tracking	Voice and video calls plus group chats Chats sync between mobile and desktop
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	Proprietary and centrally run Communities and stickers add clutter for people who only want chat
Downloadable app	Downloadable app
Open source	Closed source
License: AGPL-3.0	License not stated
Account needed	Not stated if an account is needed
Needs internet	Needs internet
Official website Full listing and sources Checked September 20, 2026	Official website Full listing and sources Checked September 23, 2026

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