The Dude - MikroTik is a Latvian company which was founded in 1996 to develop routers and wireless ISP systems. MikroTik now provides hardware and software for Internet connectivity in most of the countries around the world.
SevOne - SevOne provides network managers with monitoring, troubleshooting, and performance reporting capabilities.
Pandora FMS - Pandora FMS: Opensource monitoring software
cStatus - Monitor and scan a network.
Obkio - Simple Network Monitoring and Network Troubleshooting software to empower users to identify and troubleshoot network & application slowdown from the end-user perspective.
OpenNMS - Project home page of OpenNMS - a java based network managememnt platform developed under the Open Source model