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

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

Pallet

A tool to provision and maintain servers across various cloud platforms as well as virtual machine platforms, without any dependencies. Provides cloud and operating system independence.

     

linux windows osx open-source cloud-paas clojure

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