Signal Private Messenger for iOS provides end-to-end encrypted chat and voice calls, so you can communicate with friends without worry.
End-to-end encryption: Communications are encrypted end to end, and none of your data is saved on Signal's server.
Screen security: Signal also offers a feature called Screen Security, which prevents anyone from taking screenshots of your messages. To enable this option, go to Settings, Privacy, then Enable Screen Security.
Clear History Logs: Under Settings, you can tap Clear History Logs every once in a while to delete your message, attachment, and call history.
Private or group chat: Signal allows you to create encrypted groups for secret conversations with multiple people. Better yet, the app doesn't retain any group metadata on its server.
Lightning-fast messaging: In testing, messages were delivered almost instantaneously.
Open source: Signal's code is open source, which means that it's available for audit. Check it out at GitHub.
Bare bones messaging: Whereas competing apps enable you to send everything from GIFs and emoticons to voice messages, payments, and location info, Signal only enables you to send texts, photos, and videos.
Poor call quality: In testing, we were not wowed by Signal's lackluster call quality.
While Signal for iOS isn't as feature-rich as competing apps, it is strong on privacy. So if you want to keep your communications private, then you should definitely give it a try.