NRPE and NSClient allow you to remotely execute either pre-configured tasks or custome scripts to trigger alerts or as the result of an event (eg. an EventHandler).

NRPE Plugin
http://sourceforge.net/project/showfiles.php?group_id=26589

NRPE allows you to remotely execute Nagios plugins on other Linux/Unix machines. This allows you to monitor remote machine metrics (disk usage, CPU load, etc.). NRPE can also communicate with some of the Windows agent addons, so you can execute scripts and check metrics on remote Windows machines as well. A windows utility called NSClient is also available to accomplish the same thing on Windows hosts.

NSClient Plugin
http://trac.nakednuns.org/nscp/downloads
NSClient++, aka NSCP, aims to be a simple yet powerful and secure monitoring daemon for Windows operating systems. It is built for Nagios, but nothing in the daemon is actually Nagios specific and could probably, with little or no change, be integrated into any monitoring software that supports running user tools for polling.