Party with a Local - Party with a Local is a free app that connects travelers with locals that want to party.
Postcrossing - A postcard exchange project that invites everyone to send and receive postcards from random places in the world. For free!
Project Fixup - Meet people, not profiles
BookCrossing.com - It's the World's Library. It's a smart social networking site.
Palaround - Meet people you should be friends with.
InterPals - InterPals is a friendly community of over 5 million friends, language learners, travelers and penpals.