I have just installed "elgg" on my website
http://wholesalesonyps3.com so you can see it in action.
It does not have all the bells and whistles but it seems to be easy to install and get up and going, and it is completely free, so you may want to check it out.
You can download this free software at :
http://elgg.org/
Here is another freebie I found :
http://www.boonex.com/products/dolphin/