This application is another example of the trend toward distributed and decentralized services. "Delta Chat is like Telegram or Whatsapp but without the tracking or central control. Delta Chat does not need your phone number... Delta Chat doesn’t have their own servers but uses the most massive and diverse open messaging system ever: the existing e-mail server network... Chat with anyone if you know their e-mail address, no need for them to install Delta Chat! All you need is a standard e-mail account." Maybe this will become popular, maybe it won't, but it does show we don't need centralized servers to make a chat system work. More.