So if you have been reading up on SharePoint Server 2013 you may have heard of people talking about communities. And you said to yourself, hold it that has been around for a while now. You just need to download this or install that and it works great.
We have built that awesome functionality in and made it simple to deploy a community space where people can find each other, share documents, discuss matters that are relevant to them, and generally act like a community. Find below some great articles about what this means in SPS 2013
Discover Answers and Share Expertise with SharePoint Communities
Overview of communities in SharePoint Server 2013 Preview
What's new in social computing in SharePoint Server 2013 Preview
Create and configure communities in SharePoint Server 2013 Preview
Very good content.