By default, we think it'll ship with a plugin to offer functionality that looks like the current popular social network sites, but plugins for other free software applications are expected.
True to GNU itself, social is licensed under the GNU Affero General Public License, and we ask that plugin creators do the same.
Why are we making GNU social? well, like many of us, we've used several different social sites over the years. From orkut, to friendster, to myspace and now facebook. Yet, when a new site appears, and everyone flocks to use it, your contacts are left behind, as well as a significant amount of your private and personal information.
Social networks should be evolving, they should allow you to control what you put into them, and you should be able to keep control of your own data, including running the same software that GNU social uses, on your own website.
The web itself is already somewhat social in this regard. emerging standards like FoAF already handle some of the basics for a better way to control your contacts, and GNU social can add some fun features of its own.
GNU social is being created, from scratch, in php for maximum portability.
PHP runs on virtually any web hosting provider we can think of.
We recommend suhosin for added security.
Better for who? Look at the success of phpBB and Wordpress -- PHP is pretty much everywhere, and while maybe your favourite language is more elegant, PHP is largely ubiquitous.
Maybe everyone in the world won't use this, but not everyone uses Facebook either. Privacy is important, and lots of people value their privacy as well as their freedom to ensure the software they're using isn't doing things they don't want.