Miniature Mail - Little letters printed on demand and sent in tiny envelopes.
Party with a Local - Party with a Local is a free app that connects travelers with locals that want to party.
MailThis - Send mail from your computer
Triip.me - The happiest way to travel in 227 countries
The Simple Postcard - Text a photo to mail it as a postcard
HeyLets - The recommendation engine that lets people to see the hot local spots in their city.