This one utilizes javascript objects and simply sends the request. It is your job to write the return function(s). The library is very well thought out and brought into a very nice functioning library (sorry to say but more functional that my v1 was going to be)!

Here is an example of how they run the process:
AjaxRequest.get(
{
'onSuccess':function(req){ document.forms[0].pageSource.value = req.responseText; }
}
);

Basically what you are doing is initializing a get request and onSuccess that function is ran. Very simple and not complex. Most of the time implementing AJAX by using a different library may cause many faults as the complexity of the library requires building php objects or js objects for each individual item. This I find is much easier and much easier to maintain. It really goes to show that the KISS rule is definitely a must!

Go see the Ajax Toolbox