Messages (Google)
Messages is an instant messaging application developed by Google for the Android operating system.

Overview
It supports SMS, MMS and RCS messaging. A web interface and a Wear OS interface are also available. 

Launched in 2014, it has supported RCS messaging since 2018. By April 2020, the app had more than a billion installs. It includes a variety of integrations with Google Calendar, Google Assistant, and Google Duo.

History
The original code for Android SMS messaging was released in 2009 integrated into the Operating System. It was released as a standalone application independent of Android with the release of Android 5.0 Lollipop in 2014, replacing Google Hangouts as the default SMS app on Google's Nexus line of phones.

In 2018 the system evolved to send larger data files, sync with other apps, and even create mass messages. This was in preparation for when Google launched messages for web.

In December 2019, Google rolled out support for RCS messaging (under the name chat features) in the United States, United Kingdom, France and Mexico. This was followed by a wider global rollout throughout 2020.

The app surpassed 1 billion installs in April 2020, doubling its number of installs in less than a year.

Initially, the app did not support end-to-end encryption. In June 2021 Google introduced end-to-end encryption in Messages, supported only if two users are on Messages in a 1:1 chat (not group chat), both with RCS turned on. All one-to-one RCS-based conversations between users of Messages are end-to-end encrypted by default using the Signal Protocol.

Beginning with the Samsung Galaxy S21, Messages replaces Samsung's in-house Messages app as the default messaging app for One UI in selected markets. In April 2021, the app began to receive a modification to its user interface in markets outside of the U.S. when running on recent Samsung phones, which adheres to its use of larger headers within in-house apps to improve ergonomics.

Features
The app supports Rich Communication Services (RCS) using Google Jibe Platform servers, which use RCS's Universal Profile, marketed to consumers as "chat features". It also  integrates with the video calling app Google Duo. Messages is also available via the Web, which allows messages to be sent and received over the Internet, using a phone or computer connected to it.

See also
Messages (Apple)
iMessage
Google Allo
Google Chat

References

Google instant messaging software
Instant messaging protocols