Instagram allows users to communicate by posting photos and videos with captions that followers can like and comment on. Instagram has gained millions of new users each year since being purchased by Facebook, making it one of Facebook's best acquisitions. Snapchat is popular among younger users and differs from other platforms by allowing posts to only be visible for a set time period or to specific contacts, though users can also post to their public story. Twitter spreads news rapidly as tweets from one user can be seen by all their followers and further spread through retweets to additional followers.