Wikipedia
Threema
Threema is a proprietary encrypted instant messaging application for iOS, Android and Windows Phone. In addition to text messaging, users can send multimedia, locations, voice messages and files.
The name Threema is an acronym for EEEMA and stands for end-to-end encrypting Messaging Application.
Threema is developed by the Swiss company Threema GmbH. The servers are located in Switzerland and the development is based in the Zürich metropolitan area. As of June 2015, Threema had 3.5 million users, most of them from German-speaking countries.