Dozens of private messenger apps are available today; however, only one has the endorsement of both Edward Snowden and Bruce Schneier and is recommended by both the Electronic Frontier Foundation (EFF) and the American Civil Liberties Union. That app is Signal Private Messenger, developed by the non-profit Open Whisper Systems [1] for Android, iOS, and desktop environments. These endorsements are the result of not just Signal's ability to encrypt voice and text messages, but also its ability to integrate into existing interfaces for ease of installation and use.

Signal originated in RedPhone and TextSecure, two proprietary encryption tools for Android developed by Whisper Systems, founded by Moxie Marlinspike and Stuart Anderson. Whisper Systems was bought by Twitter in November 2011, and within half a year, both RedPhone and TextSecure, were released under the third version of the GNU General Public License. A year later, Marlinspike left Twitter to found Open Whisper Systems, which is funded by donations and grants, a neutrality that partially explains the high regard for its products.

Since 2013, Open Whisper Systems has merged RedPhone and TextSecure into a single application, adding encrypted group chat and gradually developing Android and iOS versions with comparable feature sets. Recently, it released a beta version of Signal Desktop [2] in the form of a Chrome app. So far, the desktop version, compared with the other versions, has a simplified feature set lacking password protection, for example. However, when linked to a mobile device, Signal Desktop provides centralized storage, as well as the increased usability of a mouse and a full-size keyboard.

[...]