ASP.NET

Strictly speaking it's an server side development framework, but it does include descent amount of javascript API. If you are familiar with ASP.NET you will know what I am talking about. For those who are new, ASP.NET does add quite a bit of javascript to the pages it serves (for causing postbacks, client side validations etc.). In ASP.NET 2.0 there more javascript goodies.

Now, the model followed in ASP.NET is quite structured, its not mandatory to follow that, but highly recommended, as it takes care of many things for you. AJAX can be made possible by defining 'WebMethods' in serverside code of an *.aspx page:

[WebMethod]
   public string GetHelloString(string name) 
   {
       return 'Hello '+name;
   }

<script language="JavaScript" type="text/javascript">

function GetMoreInfo() 
{
    PageMethods.RetrieveMoreInfo(
            'Geek',       
            OnComplete, 
            null);
    return false;
}
</script>