Loader.io - Loader.io is a simple cloud-based load testing service
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.
WebLOAD - WebLOAD - The most flexible and cost effective software for enterprise load, stress and performance testing, integrated with DevOps processes. Click for details
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.
Apache JMeter - Apache JMeter™.
Zabbix - Track, record, alert and visualize performance and availability of IT resources