NTPmon is a Web-based monitor for (usually LAN-based) NTP servers. It provides a small number of health metrics that help to locate NTP configuration or operational trouble spots. It uses RRDtool as its storage and graphing engine, and provides a CGI script for viewing the results.
LibreNMS is an autodiscovering PHP/MySQL-based network monitoring system forked from Observium. It aims to be easy to use and painless to deploy, and to support monitoring of a wide range of devices. Observium's license changed to a modified QPL license in May 2012, then was split into free and commercial versions. The aim of LibreNMS is to continue to create a usable NMS, but with a community focus and GPL licensing.
I don't think that "free for non-commercial use" is a very accurate description of the license in the Sleepycat Berkeley DB distribution. As far as i can tell, it is compliant with the Open Source definition (they certainly claim that it is).