What kind of web pages do you think of that routinely need to run lots of JavaScript in the background without user interaction? Or, maybe a simpler question:

What kind of web pages do you think of that routinely need to run lots of JavaScript in the background without user interaction? Or, maybe a simpler question: What web applications do you think of that routinely need to run lots of JavaScript in the background without user interaction? Right now I can only come up with games and simulations.