The main control is the BusyBox control, which can be used to show a customizable box inside web pages during time consuming activities, a very useful behavior especially during long processing tasks, in order to inform the user that something is actually happening. Typical time consuming tasks are file uploads, complex queries against databases, heavy load operations in application code, or heavy pages which require some time to be rendered by the browser.
So, if you need to implement such functionalities in your web applications you should give BusyBoxDotNet a try!
Here is a screenshot of what the BusyBox control looks like when drag 'n dropped in a page:

If you don'y like it, bear in mind that BusyBoxDotNet has many customization options which allows you to get exactly the effect you want. More info at : http://busyboxdotnet.qsh.eu/