Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Charts Factory - Create simple charts super fast and for free!
AppDynamics - Get real-time insight from your apps using Application Performance Management—how they’re being used, how they’re performing, where they need help.
ZingChart - ZingChart is a fast, modern, powerful JavaScript charting library for building animated, interactive charts and graphs. Bring on the big data!
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Google Charts - Interactive charts for browsers and mobile devices.