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Threema is a paid cross-platform encrypted instant messaging app developed by Threema GmbH in Switzerland and launched in 2012. The service operates on a decentralized architecture and offers end-to-end encryption. Users can make voice and video calls, send photos, files, and voice notes, share locations, and make groups. Unlike many other popular secure messaging apps, Threema does not require phone numbers or email addresses for registration, only a one-time purchase that can be paid via an app store or anonymously with Bitcoin or cash. Threema is available on iOS and Android, and has clients for Windows, macOS, Linux, and HarmonyOS and can be accessed via web browser but requires a mobile app to function.