AWStats is a free statistics package, written in Perl, distributed under the GNU General Public License. It can work from the command line or as a CGI script with browser interface. It can track web, streaming, ftp and mail server statistics.
AWStats is a fairly standard log analysis tool. The main interface is a single-page summary of the stats for any selected month. The page is divided into sections which provide summaries of various statistics, e.g. daily visits, referrers, search terms, etc. Links are provided from each section for more detailed stats. The illustration on the right shows some of the main page layout (the actual main page is much longer).
Stats are updated daily by default. The server admin can allow each domain user to manually update stats.
The single-page display works well, providing a lot of useful information economically. I found it a nice balance between providing all the information you need most often, and keeping the page size manageable.
You can display statistics for one month at a time, as well as viewing the year-to-date summary which is always at the top of the page. While this is a great way to view monthly and annual statistics, it is quite limited if you want to view a particular time period. There is no option to view a custom time period or even common periods such as "last 7 days".
Detailed stats are cut off after a certain point, so if you have a large or busy website you can't see a complete list of some stats. For example, the full list of referrers might go to a few thousand and the last entry is "Others", which shows a total for those referrers not included.
Despite the limitations, AWStats is one of the best all-round stats packages I have tried. It is not as feature-rich as VisitorVille or Google Analyticsbut it is a good compromise between features, ease of use and reliability. AWStats is one of the few packages I've used which has never caused a single problem.
AWStats is also strongly recommended in webmaster forums. On one hand you might want to take this with a grain of salt (there are many possible reasons for it being popular in these forums) but still, if it wasn't good, it wouldn't be getting so many unchallenged endorsements.