The Washington Post and a small group of other news organizations, including The Wall Street Journal, NBC Nightly News and Nieman Journalism Lab, are experimenting to see if the Yo app can help drive traffic to news stories, reports Cory Blair. Yo, developed in eight hours and launched on April Fools Day, 2014, now has more than 2.6 million downloads and 1.2 million active users, Blair notes.