Probe is a website-usage analysis tool. It 'probes' (logs) certain pages being viewed by a visitor, without needing access to log files from the webserver, and produces a web-page with statistics using bargraphs.
@1 Current Visitors Online shows the number of
visitors to your Website within the past x minutes,
hours, or days. If the SSI tag is only placed at the
main page of the Website, the display should
read: "There were X visitors reaching this page
since the past Y minutes".