The CJ Users Online script shows how many users are on your website. You can change the time in which the MySQL Database Table is refreshed so you can count users online per minute, hour, week etc...! As mentioned you will need one MySQL
Developer: cj-design.com Platform: Unix Date upd:2003-04-11 Hits3730 [Visit]

Easy Installation. Flat file system (no database needed). Display visitor data as text or images. Show the number of users currently online. Show unique IP counts for Today, Yesterday and Total. Optional email notification upon reaching milestones. <br /><br /> Based on Simon Stenhouse's
Developer: RT Cunningham Platform: linux, windows Date upd:2006-07-12 Hits4989 [Download] [Visit]

Easy Installation. Flat file system (no database needed). Display visitor data as text or images. Show the number of users currently online. Show unique IP counts for Today, Yesterday and Previous, and Total. Show the current IP address of a visitor. Optional email notification
Developer: RT Cunningham Platform: linux, windows Date upd:2006-09-08 Hits2806 [Download] [Visit]

FWCounters is a simple hit counter hosting service. Features text based and image based hosting with hundreds of different counter styles, no mysql required, optional hide counter from visitors. All counts are stored in a simple text file. Users refer to a script hosted
Developer: Micheal Frank Platform: linux, windows, freebsd Date upd:2005-04-16 Hits3843 [Visit]

phpVisitors is tiny php/mysql scripts which is will count visitors and pageviews of your webpage. Results will be stored into mysql database. phpVisitors is easy to install.
Developer: skintech.org Platform: php / mySQL Date upd:2003-12-09 Hits1366 [Download] [Visit]