Sensu is an great monitoring framework. Essentially, Sensu takes the results of check scripts run across many systems, and if certain conditions are met; passes their information to one or more handlers. Checks are used, for example, to determine if a service like Apache is up or down. Checks can also be used to collect data, such as MySQL query statistics or Rails application metrics. Handlers take actions, using result information, such as sending an email, messaging a chat room, or adding a data point to a graph. There are several types of handlers, but the most common and most powerful is pipe, a script that receives data via standard input. Check and handler scripts can be written in any language, and the community repository continues to grow!