You are planning to build a community/social network? if YES, here is your solution: WordPress + BuddyPress + BBpress
“WordPress is web software you can use to create a beautiful website or blog. We like to say that WordPress is both free and priceless at the same time.
The core software is built by hundreds of community volunteers, and when you’re ready for more there are thousands of plugins and themes available to transform your site into almost anything you can imagine. Over 60 million people have chosen WordPress to power the place on the web they call “home” — we’d love you to join the family.”
Official website: http://wordpress.org/
Might be you think WordPress is for bloggers only. BUT NOT anymore, WordPress is most powerful web software nowaday, you can customize WordPress for most of your projects. Fully customize and have alot plugins.