We have so enjoyed Post Crossing (postcrossing.com). We mail out cards to an assigned address, which also features a profile on the person, and they register our card number and then we get a card from someone else. Sometimes we get and send replies to the same people.
Today we got cards from a 12-year-old boy in Finland, Joosua, and a 23-year-old girl in Shanghai, China, Iris, who was actually vacationing on Hainan Island for Spring Festival. She was someone we sent a card to, so who didn't owe us one, but she was excited to get a card from two girls in America who came from China! The postcard had elephants on it so Lily was thrilled! She signed it with a cute little chop. Tomorrow cards are going out to another US state and to Germany. Finland and Germany are the most common countries participating it seems, though we have sent one to Japan that never got registered as received, and received one from Canada. It's helped the long months at home have some anticipation as we head for the mailbox every day.