Skuuddle is an app that aims to expand your active social circle. The app does it by mining your phonebook/Facebook contacts. You can categorize people into groups depending on how well you know them.

When you're making a plan to do something (throw a party, go see a movie or gig, for example), you can send out an invite to whichever group you choose. At that point, invites are sent out randomly (you can also choose instead to handpick who you invite) to those in that group. It's kind of like social potluck. Let serendipity choose who you end up hanging out with.