Google Hangouts

Google Hangouts is a cross-platform messaging app developed by Google. Originally a feature of Google+, Hangouts became a stand-alone product in 2013, when Google also began integrating features from Google+ Messenger and Google Talk into Hangouts. In 2017, Google began developing Hangouts into a product aimed at enterprise communication, splitting into two products: Google Meet and Google Chat. Google has also begun integrating features of Google Voice, its IP telephony product, into Hangouts, stating that Hangouts is designed to be "the future" of Voice. Google began transitioning users from the "classic" version of Hangouts to Meet and Chat in June 2020, and announced in October 2020 that Google Chat would eventually be made free to consumers and fully replace Hangouts, shortly after Google Meet became free as well. Google Hangouts will remain a consumer-level product for people using standard Google accounts.
History.
Prior to the launch of 
Hangouts, Google had maintained several similar, but technologically separate messaging services and platforms across its suite of products. These have included the enterprise-oriented Google Talk (based on XMPP), Google+ Messenger, and the Hangouts feature of Google+, which provided chat, voice, videoconferencing features. However, its increasingly fragmented and non-unified suite of messaging offerings was also facing growing competition from services such as Facebook Messenger, iMessage, and WhatsApp. A decision was made to scrap the existing Google Talk system and code a new messaging product through a collaboration with multiple development teams.
Following reports that the new service would be known as "Babel", the service officially launched as Hangouts during the Google I/O conference on May 15, 2013.
On February 16, 2015, Google announced it would be discontinuing Google Talk and instructed users to migrate to the Hangouts app on the Chrome browser instead.
In January 2016, Google discouraged using Hangouts for SMS, recommending to instead use Google's "Messenger" SMS app.
In May 2016, at Google I/O 2016, Google announced two new apps: Google Allo, a messaging app with AI capabilities (AI-powered bots and selfie features) and Google Duo, a video calling app. Google's Pixel and Pixel XL smartphones released later that year were the first Google devices shipped with Duo and Allo preinstalled instead of Hangouts. Google has since confirmed that the new apps will not replace Hangouts; Hangouts will remain a separate product. In December 2018 Google announced Allo would be discontinued in March 2019 with some of its features migrated into Google Messages.
On August 15, 2016, Google announced that Hangouts on Air would be discontinued on September 12, 2016, and would be folded into YouTube Live, but later on September 11, 2016, Google said the Hangouts on Air shutdown date would be moved up from "September 12, 2016" to "August 1, 2019", to free all some livestreams on YouTube. Users will have to switch to other livestream programs.
On January 6, 2017, Google announced that the Google Hangouts API would shut down on April 25, 2017.
On March 9, 2017, Google announced that Hangouts would be targeted at business users with the Hangouts brand divided into two products: Hangouts Meet (now Google Meet) and Hangouts Chat (now Google Chat). Meet would focus on video conferences and Chat would be focused on instant messaging with additional features such as bot assistant and threaded messaging. The features would be targeted at business customers while consumer versions would use a freemium model. Google stated in December 2018 that "classic" Hangouts would be disabled by October 2019.
In November 2018, the desktop Chrome app version of Hangouts started displaying these banner messages at the top of its window: "The Hangouts Chrome app will be replaced by the Hangouts Chrome extension soon." This has generated many negative user reviews on the Chrome Web Store pages for both the Hangouts extension and the app.
In August 2019, Google announced that the G Suite version of Hangouts would be replaced by "Meet" and "Chat," and push the shut down to June 2020.
In April 2020, in response to COVID-19, Google Meet became free for all users, and in October Google announced that Chat would also be made free to everyone and replace "classic" Hangouts by 2021.
In April 2021, Google Chat indeed became free as an "Early Access" service, for users who choose to use it instead of Hangouts. 
Features.
Hangouts allows conversations between two or more users. The service can be accessed online through the Gmail or Google+ websites, or through mobile apps available for Android and iOS (which were distributed as a successor to their existing Google Talk apps). However, because it uses a proprietary protocol instead of the XMPP open standard protocol used by Google Talk, most third-party applications which had access to Google Talk do not have access to Google+ Hangouts.
Chat histories are saved online, allowing them to be synced between devices. A "watermark" of a user's avatar is used as a marker to indicate how far they have read into the conversation. Photos can be shared during conversations, which are automatically uploaded into a private Google+ album. Users can also now use color emoji symbols in their messages.
As with the previous Google+ Hangouts, users can also perform a group video chat with up to 10 users at a time. In 2016 Google upgraded Hangouts to 25 concurrent users in HD video for Work/Education. The new Google Hangouts app on iOS integrates a Google Voice number to some extent, but on Android the SMS support in Hangouts doesn't fully integrate with Google Voice for calls or texts. Integration was first expected by 2014 but was deprecated in January 2016. The reason for the delay appears tied to Google switching away from the XMPP protocol it used, as mentioned above.
For Google Chrome, users do not need to install a plugin. However, for Internet Explorer 11, the user must install the "Google Talk Plugin" to be able to use the video features.
In Android 4.4, Hangouts is integrated with text messages sending and receiving functions, which is the default SMS app on the Nexus 5. For other Android phones, users can choose to open the SMS function when they download the new version of Hangouts via Google Play. SMS conversations are shown in a drawer on the left side. The update also adds GIF support and a new location-sharing button, which allows the user to send their GPS location to their contacts.
Hangouts includes the ability to make free voice calls to other Hangouts users, and charges users (via pre-registered credit) to call landline and mobile phones internationally except for calls to the United States and Canada which are free of charge. Currently, Android users must have both the Google Hangouts and Hangouts Dialer apps installed if they wish to call landline or mobile telephone numbers via the public switched telephone network. Users will have to use YouTube Live for live-streaming events.
Reception.
As of May 2013, Google Hangouts faced criticism from the Electronic Frontier Foundation as they felt that Google was "moving in the wrong direction" by shrinking its support for the open standard protocol XMPP. The new protocol makes it much more difficult for multi-chat clients like Pidgin and Adium to support Google Hangouts. They must reverse engineer the protocol.
Additionally, the tight integration of Google Hangouts and Google+ can lead to the unwilling sharing of personal information with others.
On November 30, 2014, "Make Use Of" hailed Google Hangouts as the "best messaging app on Android by far".
, Google Hangouts has a score of 2 out of 7 points on the Electronic Frontier Foundation's Secure Messaging Scorecard. It has received points for having communications encrypted in transit and for having completed a recent independent security audit. It is missing points because communications are encrypted with keys that the provider has access to, users can't verify contacts' identities, past messages are not secure if the encryption keys are stolen, the code is not open to independent review, and the security design is not properly documented.