AWStats

AWStats is a Web log analysis tool (but it also analyses FTP, streaming and email). It offers static, graphical views but also dynamic views of traffic on your Web servers.

Among other functionalities, AWStats can tell you: the number of unique visitors, page views, hits, file transfers, per domain/country, host, time, browser, operating system, etc. All data are easy to access and view via graphic representation. AWStats can be launched using CGI scripts or via command line.

AWStats is an open source software under GPL license.

External sources and links:

http://en.wikipedia.org/wiki/Awstats
http://awstats.sourceforge.net/