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.
changetrack is a program to monitor changes to files. If files are modified one day, and the machine starts working incorrectly some days later, changetrack can provide information on which files were modified, and help locate the problem. Changetrack will also allow recovery of the files from any stage.
emlog is a Linux kernel module that makes it easy to access the most recent (and only the most recent) output from a process. It works just like "tail -f" on a log file, except that the storage required never grows. This can be useful in embedded systems where there isn't enough memory or disk space for keeping complete log files, but the most recent debugging messages are sometimes needed.
game control program helps you administrate gameservers (it's written for Q1 and Q3, but works for others). It is highly modular and therefore extensible. With the current modules, it can start/stop servers, create and rotate logfiles, allow remote administration via telnet, and kick misbehaving players automagically (according to a rule set).
The ip-masq-log patch can be used on a masquerading firewall (NAT) to keep a log of all the outgoing masqueraded TCP connections. It's even possible to log the name of the user who has opened the connection. This can be a useful security tool for many small networks that are hidden by a masquerading box if users cannot be totally trusted.
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.