Signal is a mobile app developed by Open Whisper Systems. The app provides instant messaging, as well as voice and video calling. All communications are end-to-end encrypted. Signal is free and open source, enabling anyone to verify its security by auditing the code. The development team is supported by community donations and grants. There are no advertisements, and it doesn’t cost anything to use.
OS: Android, iOS.
Wire is an app developed by WIRE SWISS GmbH. The Wire app allows users to exchange end-to-end encrypted instant messages, as well as make voice and video calls. Wire is free and open source, enabling anyone to verify its security by auditing the code. The development team is backed by Iconical and they will monetize in the future with premium features/services.
OS: Android, iOS, macOS, Windows, Linux, Web
Linphone is an open source SIP Phone and a free voice over IP service, available on mobile and desktop environments and on web browsers. It supports ZRTP for end-to-end encrypted voice and video communication.
OS: iOS, Android, Windows Phone, Linux, Windows, Mac, Browser (Web)