TextSecure and RedPhone are released as free and open-source software under the GPLv3 license. Marlinspike could help the then-startup improve its security.' Whisper Systems is acquired by Twitter, 'primarily so that Mr. Moxie Marlinspike and Stuart Anderson ( Whisper Systems) launch TextSecure and RedPhone on Android. 1.3 Since 2018: Signal Technology Foundation.As of May 2021, it was downloaded more than 105 million times. As of January 2021, the platform had approximately 40 million monthly active users. The non-profit Signal Foundation was launched in February 2018 with initial funding of $50 million from Brian Acton. Signal also has an official client app for iOS and desktop programs for Windows, macOS and Linux (although registration requires an iOS or Android device). The official Android app generally uses the proprietary Google Play Services (installed on most Android devices), though it is designed to still work without them installed.

Its mobile clients are published under the GPL-3.0-only license, while the desktop client and server are published under the AGPL-3.0-only license. Signal's software is free and open-source. The client software includes mechanisms by which users can independently verify the identity of their contacts and the integrity of the data channel. Signal uses standard cellular telephone numbers as identifiers and secures all communications to other Signal users with end-to-end encryption. It can also be used to make one-to-one and group voice and video calls, and the Android version can optionally function as an SMS app. Users can send one-to-one and group messages, which can include files, voice notes, images and videos.

Signal is a cross-platform centralized encrypted instant messaging service developed by the non-profit Signal Foundation and its subsidiary, the Signal Messenger LLC.

Android signal messenger app