Anteater is a log analyser for MTA logfiles (such as those produced by sendmail and postfix). The tool is written in 100% C++ and is very easy to customize. Input, output, and the analysis are modular class objects with a clear interface. Currently, there are modules for reading the syslog format of sendmail and postfix that do up to eight useful analyses and write the result in plain ASCII or HTML, to stdout or to files.
Advanced Web Statistics (AWStats) is a free powerful Web server logfile analyzer (Perl script) that shows you all your Web statistics including visits, unique visitors, pages, hits, rush hours, search engines, keywords used to find your site, robots, broken links, and more. It works with both IIS 5.0+ and Apache Web server log files as a CGI and/or from the command line. It also supports around 40 languages.
phpOpenTracker is a framework solution for the analysis of Web site traffic and visitor behaviour. It features a logging engine that, either invoked as a Web bug by an HTML image tag or embedded with two lines of code into your PHP application, logs each request to a Web site into a database. One installation can track an arbitrary number of Web sites. Through its API, you can easily access the gathered data and perform complex operations on it (for instance, the analysis of your visitors' click paths).