collectd

A daemon that collects system performance statistics periodically, and provides tons of plugins to store and analyze these values

     

linux windows osx open-source monitoring c

Eucalyptus

An open source software for building Amazon EC2-compatible private and hybrid cloud platforms

     

linux open-source virt cloud-paas c

Instrumental

Instrumental is a real-time, high-scale application and server monitoring tool with intelligent alerts, a powerful query language, and free development accounts.

     

linux windows oxs free metrics commercial metrics monitoring visualization php ruby python net java nodejs

Monit

An open source utility for managing and monitoring processes, programs, files, directories and filesystems

     

linux osx open-source monitoring process-mgmt c

Nagios Core

Nagios Core network monitoring software is a powerful, enterprise-class host, server, application, monitoring and alerting tool

     

linux solaris bsd open-source monitoring c

Netdata

netdata is a system for distributed real-time performance and health monitoring. It provides unparalleled insights, in real-time, of everything happening on the system it runs (including applications such as web and database servers), using modern interactive web dashboards.

     

linux open-source monitoring c python

Rex

A agent-less server orchestration tool built on Perl

     

linux windows osx open-source orchestration perl

Zabbix

An open source, enterprise-class monitoring framework

     

linux windows osx open-source monitoring c