Postcrossing - A postcard exchange project that invites everyone to send and receive postcards from random places in the world. For free!

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.

swap-bot - Swap-bot is a online service that organizes group swaps and a community of creative individuals.

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.

BookCrossing.com - It's the World's Library. It's a smart social networking site.

Anygram - Anygram app offers features that let you meet new people so you can make new foreign friends practice native languages to learn something new.