What you can do
You can download NetXMS, run it on as many systems as you like, at home or in a business, without paying anyone or asking permission. You can read the source code, change it, and pass on copies, modified or not.
The one obligation comes when you distribute it: whoever receives NetXMS from you, changed or unchanged, must get the same freedoms, including access to the source code of your changes. Running a modified version inside your own organisation does not count as distributing it.
GPL and LGPL, which parts
The server, the agent, subagents, database drivers, notification channel drivers and command-line tools are under the GNU General Public License, version 2 or, at your option, any later version. That is the license the whole product is usually described by: GPLv2.
Most of the shared libraries (libnetxms, libnxsl, libnxsnmp and other libnx* libraries; COPYING has the exact list) are under the GNU Lesser General Public License, version 3 or later. The LGPL lets you link your own program against these libraries without your program itself becoming GPL, as long as the libraries stay LGPL and any changes you make to them are shared.
Third-party code
The source tree bundles some third-party components, each under its own license. The full per-component list is in the COPYING file, next to the complete texts of the GPL and the LGPL .
Enterprise Edition
NetXMS Enterprise Edition is a separate, commercially licensed build sold by Raden Solutions. Nothing about it changes the Community Edition's license: the open-source release stays GPLv2. The editions page lists what differs.
Trademark
The license covers the code, not the name. NetXMS and the NetXMS logo are trademarks of Raden Solutions.
This page is a summary written for people, not a license. Where it and the license texts differ, the license texts govern.