The LogAnalyzer project provides an easy to use but powerful frontend for
searching, reviewing and analyzing network event data, including syslog,
Windows event log and many other event sources. It focuses on the
user-interface side of this project, so the data itself needs to be
gathered by another program, for example the stock syslogd, rsyslog (often
the distro's default syslogd), WinSyslog or MonitorWare Agent. LogAnalyzer
works equally well on Linux and Windows.

LogAnalyzer is a free, GPLed open source application written mostly in php.
Data can be obtained from databases but also from plain text files, for
example those that are written by the syslogd.