Prometheus is an open source monitoring system originally built at SoundCloud. It collects metrics from configured targets at given intervals, evaluates rule expressions, displays the results, and can trigger alerts if some condition is observed to be true. Its features include a multi-dimensional data model, flexible query language, autonomous single server nodes, and multiple modes of graphing and dashboarding support.
Many DevOps organizations are moving towards Prometheus because it is native to containerized environments and integrates with Kubernetes.