IT Infrastructure Monitoring

https://www.nagios.org/
https://assets.nagios.com/downloads/nagioscore/docs/nagioscore/4/en/toc.html

http://www.zabbix.com/
https://bosun.org/
https://www.icinga.com/
http://www.cacti.net/

http://graphiteapp.org/


Commercial
https://newrelic.com/
https://www.appdynamics.com/
https://www.datadoghq.com/

https://www.blazemeter.com/blog/top-10-monitoring-tools-every-devops-needs
http://blog.takipi.com/7-monitoring-tools-to-prevent-the-next-doomsday/
https://haydenjames.io/20-top-server-monitoring-application-performance-monitoring-apm-solutions/
http://www.infoworld.com/article/2683857/network-monitoring/article.html#slide4

For Azure
https://github.com/MSOpenTech/wamo
https://www.savision.com/resources/scom-solarwinds-nagios-azure-complete-monitoring-2
http://cloudmonix.com/blog/the-ultimate-list-of-top-azure-monitoring-tools/