NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Blumira - Blumira's threat detection platform offers both automated threat detection and response, enabling organizations of any size to more efficiently defend against cybersecurity threats in near real-time.
Network Server Suite - Network Server Suite is a network server monitoring software for Windows, Linux, or AIX that manage all of network servers, services, applications, and devices from a single, mobile-ready console.
Google StackDriver - Stackdriver provides monitoring services for cloud-powered applications.
mackerel.io - mackerel.io is a server and application performance monitoring platform.
Devo - Devo delivers real-time operational & business value from analytics on streaming and historical data to operations.