Concept Board, a collaborative online whiteboard that I reviewed in August, recently released a Google Chrome App that integrates with Google+ Hangouts. Concept Board for Google+ allows you to collaborate on mind maps and other whiteboard activities through Google+ Hangouts. Invite your collaborators to hangout with you on Google+ and you can talk while developing a mind map or other diagram together. The video below offers a demonstration of Concept Board for Google+.
Applications for Education
Concept Board for Google+ could be a great way for students to collaborate on the development of an outline for a group project. By using Google+ Hangouts students can quickly make clarifications to each other regarding the various elements of the mind maps that they've created.