RapidSpike - RapidSpike is an uptime and performance monitoring service for websites and web applications.
Nagios - Complete monitoring and alerting for servers, switches, applications, and services
Monitis - Monitis specializes in IT monitoring, covering server, website, app monitoring and more within an all-in-one monitoring platform.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Raygun - Raygun gives developers meaningful insights into problems affecting their applications. Discover issues - Understand the problem - Fix things faster.
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.