Source: http://www.engadget.com/2015/11/19/google-now-lets-you-join-hangouts-as-a-guest-no-account-needed/
The worst thing about organizing an online meeting is squabbling over platform. Should you choose WebEx? Skype? Google? Your decision just got a little easier. As of today, you no longer need to have a Google account to join a meeting Hosted on Hangouts -- just a link.
Source: Google