Applets provide features like custom data streaming, graphic manipulation, threading, and advanced GUIs which AJAX cannot.
However, with the help of DHTML, the functionalities of AJAX can be extended further.
AJAX requires that the browser be DHTML and AJAX capable.
AJAX-based functionality does need to take browser differences into consideration due to which using a JavaScript library such as Dojo which abstracts browser differences is recommended.
AJAX/DHTML works well for applications where the latest browsers are used.
