Google just launched a new version of Hangouts that integrates it right into the Gchat spot on your inbox. For the most part, the Gchat experience is mostly the same, but there's one new feature that functions very differently. Your "buddy list" isn't just your contacts, it's a rolodex of all of Google+.
Type in a name into the chat search box, and it'll first give you results for people you know, and then starts giving you relevant results for strangers. When I tried searching first names using a dummy Gmail account with no friends or contacts, I still got tons of results for complete strangers, including famous people. It prioritizes verified or popular users when searching by first name only.
Basically, Hangouts is a White Pages that gives you access to Gchat anyone with a Gmail address. You don't need to know their email address, just a name. The ability to search out and then ask to chat strangers already existed in the Google+ world, but not right inside your Gchat window that lives inside your inbox.
Let's have some fun.