LINE is a chat software that combines Skype, WhatsApp and a bit of Facebook. Forever free and it’s Japanese made. It works on Android, iOS and BlackBerry phones as well as Windows desktop computers (linux with emulator).
You can create account with phone number, Facebook connect or email. Once you have one, you can add friends by inserting in the “Add friend by ID?
Real time communication, specially with smartphones. We use it to coordinate ourselves in the streets, exchange multimedia or just because is better than SMS (In Spain, for example, SMS is about to die).