Discord is like a mix of skype, teamspeak, & IRC (the old internet relay chatrooms) - it also just opened up a game store too. I've been using it for about 3 years or so - they are good for social interaction stuff & for creating a community around your product/clan/group/whatever.
Link is in the footer, icon to the right of the twitter one - recommend installing the desktop app as opposed to using the web browser version.
Mmm ok, world goes fast, myspace, facebook, tweet, reddit now this discord... I m gonna check it out.