LMon is a package for near real-time monitoring of logs, sending email alerts
upon known (rule hits) or unknown data (rule misses). It features buffering of
multiple rule hits within a given interval, cap at a given maximum number of
lines, wait for a given interval before sending next alert, and auto- discovery
of log rotation. It can be run from the command line without configuration, or
be controlled from a central configuration file with multiple instances
monitoring different log files/sending alerts to different people.

WWW: http://www.bsdconsulting.no/tools/