I guess you mean web analystics software. Well the best around is urchin , and if you have a dedicated server with ev1servers or servermatrix you will get a 100 domains licence for free as far as i know,if you don`t you will have to pay almost 800$ for it (i guess) . I saw that you are seeking for free software , the most popular are awstats ( http://awstats.sourceforge.net/ ) and webalizer ( http://www.mrunix.net/webalizer/ )
