AWStats is a free powerful and featureful server logfile analyzer that shows you all your Web/Mail/FTP statistics including visits, unique visitors, pages, hits, rush hours, os, browsers, search engines, keywords, robots visits, broken links and more
DetectBrowser is Perl module which detects user's browser and OS, by analyzing the HTTP user-agent string. It recognizes all versions of AOL,Konqueror,MSIE,Mozilla,Netscape,Opera,WebTV,etc... running on BSD,HP-UX,Linux,Mac,Sun,Windows,etc...
ToGather is a network statistics tool (RRDtool frontend) and a SNMP MIB browser.
ToGather is OS independent as it uses the programming language perl and any web browser for the display
of the graphical statistics and the MIB browser.