filewatcher is a system administration tool designed to maintain an archive of changes to important system files (or any interesting file) and to send details about changes to one or more e-mail addresses when they are detected [More Info]
Nagios Template Config Merging Tool (download)
This utility takes large/verbose config files created by the convertcfg utility (which is distributed with Nagios) and merges/squashes them to make use of templates and eliminate duplicate directives in definitions.
This Perl script allows you to submit external commands to Nagios easily from a script or the command line. Includes support for most all external commands supported by Nagios. It can also generate a quick text-only overview of current problems. Note that the version posted here is somewhat stale and needs to be rewritten to work with Nagios 2.x and Nagios 3.x.