Clusto is a cluster management tool. It helps you keep track of your inventory, where it is, how it's connected, and provides an abstracted interface for interacting with the elements of the infrastructure.
Clusto is used by several companies to help mantain their internal infrastructure. It was first used to manage digg.com's infrastructure but since then more people have started to use and contribute to the project.
Clusto's original author is Ron Gorodetzky but an assortment of individuals have contributed to its growth. Take a look at the nifty github contributors graph if you want to get a full list of people who have sent patches.