Overnight - Book a last minute room with locals, in seconds.
BookCrossing Core - Create own BookCrossing site based on Drupal CMS.
FriendsTonight - Meet new friends to join your friends, tonight
Postcrossing - A postcard exchange project that invites everyone to send and receive postcards from random places in the world. For free!
Facebook Local - Discover places to go and events happening near you
Linear - Streamlined issue tracking for software teams