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Signal vs Duetto: catalog facts
Signal	Duetto
Free Free; developed by a nonprofit funded by grants and donations	Free Free and open source under the GPL 3.0 or later.
Android, iOS, Windows, macOS, Linux	Android, Self-hosted
End-to-end encryption on every message and call using the open source Signal Protocol No ads, affiliate marketers or tracking	End-to-end encrypted audio and video Always-on channel with no calling step
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	Limited to two people by design Very new project with little track record
Downloadable app	Downloadable app, Self-hosted
Open source	Open source
License: AGPL-3.0	License: GPL-3.0-or-later
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 October 2, 2026

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