BookCrossing Core - Create own BookCrossing site based on Drupal CMS.
Frysbe - Frysbe: Make global friends at random and the fling app comes up with features to send messages to strangers from every corner of the world to expand your social circle.
BookMooch - BookMooch is a community for exchanging used books.
Yochat - Yochat app enables users to get to know about strangers from a large number of countries from around the world by video chatting with them.
swap-bot - Swap-bot is a online service that organizes group swaps and a community of creative individuals.
PenPal World - Connect with people all over the world