The Signal Foundation and Signal Messenger created Signal, a cross-platform encrypted communications service. One-to-one and group messages, which can include files, voice notes, photos, and videos, can be sent using the Internet. The Android version can potentially serve as an SMS app, and it can be used to make individual and group audio and video calls.
Standard cellular phone numbers are used by Signal as IDs, and end-to-end encryption is used to protect all communications with other Signal users. The apps have features that allow users to independently confirm the legitimacy of the data channel and the identity of their contacts.
The software used by Signal is open-source and free. The server code is released under the AGPLv3 licence, while its clients are released under the GPLv3 licence. For features like push notifications, the Android app typically uses the exclusive Google Play Services, which are pre-installed on most Android devices. The app provides its own fallback open-source version of the required functions, so it can still operate in full on a phone without these installed.
With an initial investment of $50 million by Brian Acton, the nonprofit Signal Foundation was established in February 2018. On Android, Signal has received over 10 million downloads.
On iOS, Android, and PC, Signal users can place individual and group voice and video calls to other Signal users. Group calls can accommodate up to 5 persons, with intentions to increase that number. All calls, including long distance and international calls, are made via a Wi-Fi or data connection and are cost-free (data rates not included). On iOS, Android, and a desktop client, Signal users can send text messages, files, audio notes, images, GIFs, and video chats to other Signal users over a Wi-Fi or data connection. Additionally, the software offers group chatting.