WHMCS - WHMCS is an all-in-one client management, billing & support system for online businesses.
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.
HostBill - HostBill is a powerful and flexible, all-in-one automation, billing, client management and support platform for online businesses.
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.
Blesta - Blesta is professional client management, billing, and support software.
Zabbix - Track, record, alert and visualize performance and availability of IT resources