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.
Pandora FMS - Pandora FMS: Opensource monitoring software
cStatus - Monitor and scan a network.
OpenNMS - Project home page of OpenNMS - a java based network managememnt platform developed under the Open Source model
Trafikito - Monitor CPU, RAM... or output of any command and make API call on event, default is email messages.
CloudView NMS - CloudView is a standards-based network management and monitoring system (NMS).