Anyone looking to keep in touch with friends and family far away may want to check out WhatsApp, a handy messaging and calling app. Popular outside of the United States, WhatsApp allows users to share text messages, photographs, and videos with one another using WiFi, thus eliminating SMS fees. Free to download, WhatsApp can be used on iPhone, Android, and Windows phones as well as on desktop computers. In addition, users can share documents of 100mb or less.