The features of the app include one-on-one, as well as group calls. It works by determining and making the user see who is online or available. If a particular user is online, then you can call them instantly. Since CatchUp is not synched with Facebook, therefore having a Facebook account is not required to use it. The app accesses and retrieves your phone contacts in order to build your buddy or friends list.
So that's kind of an advantage. Imagine having over a 1,000 friends on Facebook and having all of them being able to call you easily on CatchUp, that would indeed be a total disaster. The idea on which Facebook based CatchUp was that people are sometimes hesitant about calling another person at a time that may be inappropriate. This means that sometimes when you want to call another person, you are not sure whether they are actually available to talk or not.
It Is too early to say if CatchUp would be as successful as the rest of the Facebook-owned apps, namely Instagram and Whatsapp. It is also unlikely that CatchUp would remain a standalone app for too long, considering Facebook's approach to integrating all the apps it owns. Right now, the app is available within the United States for testing for a limited period- on Google Play and Apple's App Store for Android and iOS respectively.