Nagios is a powerful monitoring system that enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes.
Nagios vs Lansweeper opinions
Nagios has nothing to do with asset management
Easy to use configuration web interface for nagios and neamon. openITCOCKPIT is a perfomant monitoring system with support for distributed monitoring (Satellites), REST API, nice dashboards, maps, graphs and a modular concept for easy customization.
Open-AudIT is a network auditing application. It is based on the scripting languages of PHP, Bash and VBScript. It can tell you what is on your network, how it is configured and when it changes.
Kuwaiba is an enterprise grade, open source Network Inventory System (which covers some aspects of NGOSS/Frameworx), built on top of the Netbeans Platform and Java EE, focused on scalability, reliability, usability and interoperability.