Hangouts does have a Chrome app (not extension, but app). Which runs in a pop-up mode and gives a user interface similar to android.

Also, it starts up with your operating system with a floating icon which stays at top of the windows if you want, and provides notifications. Your friends can use that if they want to stick to hangouts.

[Hangouts Chrome App](https://chrome.google.com/webstore/detail/google-hangouts/nc...)