Hangouts was until recently, a combined videochat/IM/sms app for desktop and mobile, tied to your google account. If you had a Google Voice service account, it

Hangouts was until recently, a combined videochat/IM/sms app for desktop and mobile, tied to your google account. If you had a Google Voice service account, it could also be used to send SMS messages from the desktop. But then Google decided they didn't want Hangouts to be that anymore, and are stripping out features to focus it as the "corporate" messenger while they split its functionality into three different Android apps - Allo, Duo, and Messages. So now Hangouts is just a desktop/mobile videochat and IM. No more SMS. And they have a "consumer-oriented" pair of voicechat and IM apps in Duo and Allo. But they're not compatible with Hangouts so if one user uses Hangouts and the other one uses Allo, they can't communicate directly. Google has gone mad.