Online platforms are websites that allow users to create and share various types of content such as text, images, and videos. Common online platforms include social media sites like Facebook that allow sharing of content, blogging platforms like WordPress that focus on customization of design and content, and content management systems that provide tools for development of applications. Application programming interfaces (APIs) allow software programs to communicate and interact, and are commonly used in developing graphical user interfaces. Popular websites that use plug-in APIs include YouTube, Flickr, Twitter, Facebook, and Google Maps.