Tenshi is a log monitoring program, designed to watch one or more
log files for lines matching user defined regular expressions and
report on the matches. The regular expressions are assigned to
queues which have an alert interval and a list of mail recipients.

Queues can be set to send a notification as soon as there is a log
line assigned to it, or to send periodic reports.

Additionally, uninteresting fields in the log lines (such as PID
numbers) can be masked with the standard regular expression grouping
operators ( ). This allows cleaner and more readable reports. All
reports are separated by hostname and all messages are condensed
when possible.

WWW: http://www.gentoo.org/proj/en/infrastructure/tenshi/