Graphite is a free, open source tool that monitors and graphs numeric time-series data, which is typically collected from collection daemons or other monitoring solutions, such as Nagios or Prometheus. Once the data is collected, Graphite has a built-in UI that provides useful visualizations via its Django web application. Graphite can be used to track the performance of websites, applications, business services, and networked servers.
While Graphite does not provide plug-ins, there are a lot of existing tools that are Graphite-compatible. Grafana is often used with Graphite to extend its functionality.