What are some alternatives?
When comparing NetXMS and Nagios, you can also consider the following products
Zabbix - Track, record, alert and visualize performance and availability of IT resources
System Center Operations Manager - System Center Operations Manager 2012 R2 uniquely enables customers to reduce the cost of data...
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Opsview Atom - Monitor everything. Integrate anything. Scale anywhere.
Icinga - Icinga is a fork of Nagios and is backward compatible.
OpenNMS - Project home page of OpenNMS - a java based network managememnt platform developed under the Open Source model