Google has dropped the requirement of having a Google account to join a Hangouts video call, as you can now invite people without one. The way it works is simple. The meeting organizer will give out the link to the meeting, and those without an account will be prompted to enter their name and submit a request to join. Once that is entered, the organizer will receive a notification that the person is attempting to join, and can approve or deny.
In an effort to continue to make things easier, Google is also providing a link to the video call in the description of the event for those who don't use Google Calendar. The guest access feature is now available.
Source: Google Apps