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.
Postcrossing - A postcard exchange project that invites everyone to send and receive postcards from random places in the world. For free!
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.
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
Random PenPals - Get a quarantine PenPal in 10 seconds