Re: Google+ Messenger and Google Talk, What are the differences b
Google+ Messenger (formerly Google+ Huddle) is a part of the Google+ app, which is more meant to be a SMS-like service. Your conversations is always available on Google's servers, even though you decide to uninstall, and later reinstall the Google+ app again. You can also share photos, and other content, through the Google+ Messenger service, to your other Google+ circling. When you receive a Message and / or incoming Hangout, then your smartphone will ring and vibrate just as normal calls and texts.
Google Talk has been around for many years now, and is the Instant Messenger (IM) service from Google, which is available for all platforms, both in the browser, and by installed software.