Threema Alternatives for iPhone

Telegram is a free cloud-based instant messaging platform.

WhatsApp Messenger is an instant messaging platform owned by Facebook.

Slack is a cloud-based team collaboration tool.

Tox is a peer-to-peer instant-messaging and video-calling protocol that offers end-to-end encryption.

Signal is the most scalable encryption tool.

Wire is a cross-platform, encrypted instant messaging client created by Wire Swiss. It is available for iOS, Android, Linux, Windows, macOS and Web browser clients.

ChatSecure is a messaging application for iOS which allows OTR and OMEMO encryption for the XMPP protocol.

Sicher is a freeware instant messaging application for iOS, Android, and Windows Phone. Sicher allows users to exchange end-to-end encrypted text messages, media files and documents in both private and group chats.

Zulip is a chat and collaborative software.

Wickr is an instant messenger application.

Dasher Messenger provids a way to message friends.