Isoqlog is an MTA log analysis program written in C. It is designed to scan qmail, Postfix, Sendmail, and Exim logfiles and produce usage statistics in HTML for viewing through a browser. It produces a "top domains" statistic according to sender, receiver, total mails, and bytes, and keeps the main domain mail statistics with regard to day's top domain, and top users values for per day, per month, and per year.
ISPacct (formerly Brickacct) accounts the logfiles which Bintec routers spew out depending upon configurable rules. Logfile-analyzing mail accounting functionality is also included (in beta stage). It has multiple backends like text, HTML, and MySQL. It was designed and used by a small ISP and is geared towards such uses as monthly accounting per IP or per dial-in use.
LogDog monitors messages passing through syslogd and takes actions based on key words and phrases (which can be regular expressions). It has a configuration file which allows you to specify a list of key words or phrases to alert on and a list of commands that can be run when those words are encountered.
logsurfer is a log checking/auditing tool similar to swatch and logcheck but with the capability of handling multi-line messages and dynamically adapting the ruleset. It is written in portable C, well documented, fast, and flexible. It works on any textfile or stdin, can be run at intervals or continuously, and has timeouts and resource limits.
log_analysis is a log file analysis engine that extracts relevant data for any of the recognised log messages and produces a summary that is much easier to read. It can be configured to recognize entirely new log types. log_analysis natively understands about 100 different kinds of syslog messages, as well as sulog and wtmp messages for Linux, Solaris, and OpenBSD. It also has optional continuous monitoring capabilities, with both text and GUI modes.