Hangouts is coming to iOS today. At the time of this writing, it doesn’t appear that it’s available, but it should arrive at some point.
According to website TUAW, it’s basically Google Hangouts as we are used to, but for mobile. There isn’t much info on it, and it was just a minor part of the keynote at Google’s I/O conference.
Perhaps this can take off where FaceTime hasn’t yet been able to reach. While great, applications like FaceTime don’t reach other users. Skype works, but it still requires users to set up a Skype account if they don’t have one already. Almost everybody uses Gmail or a Google service in some way. Perhaps this can help increase the adoption rate.