Facebook has just launched an app to compete with Snapchat, Poke. Poke lets you “Poke” friends with a message, photo, or video. Like Snapchat, you can choose how long your friend can view your Poke. Also like Snapchat, your friends need to hold down your Poke to view it. Potentially Poke’s biggest strength over Snapchat is the built-in ecosystem of all of your Facebook friends.