Unbordered - Unbordered app comes up with features to help you in finding the perfect language practice and exchange partners so you can practice foreign languages right through your mobile phone.
BookCrossing Core - Create own BookCrossing site based on Drupal CMS.
PenPal World - Connect with people all over the world
BookMooch - BookMooch is a community for exchanging used books.
We3 - AI that finds you the most compatible people nearby
swap-bot - Swap-bot is a online service that organizes group swaps and a community of creative individuals.