#7 Zenoss:

Zenoss is primarily an open source networking application that is used for monitoring issues within the network.  The software is mainly based on Zope application server and helps IT administrators troubleshoot problems across various servers. Zenoss Core provides a web interface that allows system administrators to monitor availability, inventory/configuration, performance, and events. 90 percent of the software is written in Python while the remaining 10 percent is written in Java.

#6 Zabbix:

Created by Alexei Vladishev, Zabbix is a network management system software designed to monitor and track the status of various network services, servers, and other network hardwares. The software primarily uses MySQL, PostgreSQL, SQLite, Oracle or IBM DB2 to store data. The backend part of the software is written is C language while the front end is written in PHP. Also the software offers an agent for supporters to monitor statistics such as CPU load, network utilization and disk space. Zabbix includes support for monitoring via SNMP, TCP and ICMP checks, as well as over IPMI, JMX, SSH, telnet and uses custom parameters.