pasvnag_lite is a (passive) nagios/icinga checker. It runs nagios (or icinga, ..) checks on defined objects and submits the results to a specific NSCA host.
The config file syntax is quite similar to nagios (or icinga) one. See http://www.unixadm.org/software/pasvnag_lite/README.html
pasvnag_lite requires an NSCA host and the send_nsca binary.