BookMooch - BookMooch is a community for exchanging used books.
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.
BookCrossing.com - It's the World's Library. It's a smart social networking site.
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.
Random PenPals - Get a quarantine PenPal in 10 seconds
PenPal World - Connect with people all over the world