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Threema vs Viber: catalog facts
Threema	Viber
Paid A one-time purchase is required. Business plans are separate.	Free Free to download and use for messages and calls.
Windows, macOS, Linux, Android, iOS, Web	Android
No phone number or email required; the ID is random Apps are open source and the company is based in Switzerland	Voice and video calls plus group chats Chats sync between mobile and desktop
A one-time purchase is required for each platform Smaller user base than the mainstream encrypted messengers	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
Not stated if an account is needed	Not stated if an account is needed
Not stated if it works offline	Needs internet
Official website Full listing and sources Checked September 22, 2026	Official website Full listing and sources Checked September 23, 2026

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