Its called AjaxView and can remotely monitor any AJAX web app that is currently on the web, locally or whatever.
You basically, install a small proxy application, then change your Internet Explorer LAN connection to go through a proxy of localhost:8888.
Go and browse your web application or your own AJAX app, and execute your normal series of functionality.
Once your done, you then browse to a page generated by the tool itself
This gets you something like this:
You can then click on whatever item you want, typically the site that represents the worst performance. You'll then get something like this:
Here I have clicked on the 'Mean Time (ms)' view to get column sorted by the slowest functions. If I want to drill down a bit more, I can click on the 'Details' link which gives me:
This shows me a breakdown of which functions took how long.