Whos Amung Us is a web analytics website (that I reviewed earlier). It shows the number of visitors who are on each page of your website. All you need to do is add a few lines of code to each page that you wish to track.
The live statistics and easy setup of Whos Amung Us is addictive. However, it can be a bit tiring if you are a webmaster and only need to know the total number of visitors to your site at any given time.
The image right is that of Firefox addon, and the one below is of Chrome extension. In Chrome, it appears to the right of URL bar (as is the case for all addon buttons), and in Firefox, it is on the bottom right corner on the status bar. The Firefox extension supports tracking multiple sites, unlike Chrome.