Yo. It’s one of the simplest ways to greet someone – and now the simplest messaging app on iOS. The entire point of the app is to send your friends a push notification that just reads “Yo.” After launching as a joke on April Fool’s Day, Yo has recently gone viral and now has more than 50,000 active users. It may seem pointless, but Yo has a hidden purpose: a new type of real-time notifications – ones where the notification itself is the entire message. Right now, the Yo account WORLDCUP can send a “Yo” every time a goal is scored in a World Cup game. In the future, other companies could create similar accounts. Restaurants could “Yo” you when your table was ready, airlines could “Yo” you when your flight is boarding, or news sites could “Yo” you whenever they post a breaking news story. It’s these possibilities that have brought in more than $1 million in funding so far – and why you should download Yo and give it a shot today.