ComeStat is a lightweight service which provide a small widget for bloggers to track their visitor.
Similar with Whos.amung.us, ComStat provide a small widget for bloggers. What you need to do is just paste the Javascript code provide by them into your blog and ComStat will track the visitors for you. The button is look like this 
. It shows total connections to your website currently. When you click on the button, you can find more details, as shown in the screenshot below:
