The Naemon core is a network monitoring tool based on the Nagios 4 core, but with many bug fixes, new features, and performance enhancements. If you today use Nagios, you should switch to Naemon to get bugfixes, new features, and performance enhancements.
Rather than the Nagios way of putting everything from UI to check scheduler in one package, we like to keep things more modular. The sum of all the modules that we build and ship will give you a good monitoring suite.
Naemon is created by the community, for the community, and (soon) owned by the community ourselves. This lets us be governed by our needs, rather than corporate profit motives.