The Simple Postcard - Text a photo to mail it as a postcard
PenPal World - Connect with people all over the world
Felt for iPhone - Handwritten cards for the modern world
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.
Send Mail Get Mail - A postcard-sending website.
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.