Hoodline - Hyper-local SF news from the former editor of TechCrunch
Party with a Local - Party with a Local is a free app that connects travelers with locals that want to party.
Circa - Find a time that works for everyone, in every time zone
Palaround - Meet people you should be friends with.
The Tab - Hyperlocal news site written by student journalists
Babble - A more personalized social network