Facebook Messenger manages to compartmentalize one of Facebook's most important features and make it instantly more accessible on any mobile device. The result is a must-have app for anyone who communicates through Facebook as much as or more than they do using their phone. Using the core features of the iPhone, combined with the social tools of Facebook, it is an immediate upgrade for all of your communications tools.
Facebook Messenger is a relatively bare-bones app. After installation, you log in--an automatic process if you have Facebook log-ins stored on your phone --and you can see all of your recent messages from Facebook. Tap the top-right corner to see your contacts and tap the "Compose" button to start a new message. The real draw of this app is that, when you receive a new message, it will be instantly delivered as a notification--much as a text message or iMessage would on your phone. The result is a Facebook-style text messaging system that allows you to communicate with anyone on Facebook as you would someone on your list of phone contacts.
Facebook Messenger seems like a strange offshoot of the core Facebook product, but for anyone that uses the messaging and communications tools on Facebook frequently enough to log in to their app more than once a day, the tool is a must have. It's easy to install, easy to use, and it makes sending and receiving messages much easier for anyone with an iPhone or iPad.