The Cluster app is helping users dodge a problem that has been cropping up more and more recently. While Facebook is great and Instagram is like God's gift to photography and social media at the same time, there are still some pictures that you may not want to post. For that there are apps like Snapchat, but Snapchat's greatest strength is also a weakness in some ways.
Cluster is interesting because it lacks a complexity that many of the big time social media apps have, it does fill a need though. Those drunken photos that you don't want your potential employers to see will find a safe home on Cluster, which lets you create private groups to show exactly what you want to a certain group of people's eyes and their eyes only.