Scorpio can also handle AJAX requests.
This works best for searches or lists or code fragments (e.g. a news pop-up). You may find you have to make minor changes to have it work exactly how you want, but that is the basics.
The mvcRequest offers an isAjaxRequest method for detecting if the request was made with an AJAX header or with the parameter ajax=1 (or true).
Pre Scorpio 0.3
xajax is still available but has been moved away from the mvcControllerBase into a dedicated controller mvcXajaxController. This extends mvcController - your site specific controller and adds in the xajax methods.
You will need to add ajax routing to your controller by setting the "ajaxserver" as a valid route on the controller and then intercepting and redirecting these requests to xajax.