Netdata collects metrics per second and presents them in beautiful low-latency dashboards. It is designed to run on all of your physical and virtual servers, cloud deployments, Kubernetes clusters, and edge/IoT devices, to monitor your systems, containers, and applications.

An advanced network monitoring solution to monitor network up/downtime, traffic and usage. Features include availability, performance, and bandwidth monitoring (SNMP, WMI, packet sniffing, NetFlow), instant alerts, reporting, failover clustering.

Cabot is a free, open-source, self-hosted infrastructure monitoring platform that provides some of the best features of PagerDuty, Server Density, Pingdom and Nagios without their cost and complexity.

PHP Server Monitor is a script that checks whether your websites and servers are up and running. It comes with a web based user interface where you can manage your services and websites, and you can manage users for each server with a mobile number and email address.

Enterprise-ready monitoring solution that provides unparalleled flexibility for IT to address both immediate and unforeseen operational issues, including infrastructure and IT processes.

Monitis is a Cloud monitoring and IT analytics service offering Website Monitoring, Server Monitoring, Network Monitoring, Application Monitoring, Cloud Monitoring, and Custom Monitoring.

Open Source (GPLv3) Network Monitoring for Windows, Linux & Android. Simple setup, auto-detects running services, runs checks concurrently, open port scanning and alerting. Written in C++ & Qt 5.

Proactively monitor your websites and online services. Receive immediate notification when a problem is detected so you can quickly resolve the root cause and prevent potential escalation.