web2py is not an AJAX framework but it works with AJAX frameworks. For examples scriptaculous works great with web2py. You may also use Web2py controllers to handle JSON request/response messages. Web2py also come with some a view called "web2py_ajax.html" included by "layout.html" that provides popup, collapse, fade effects and an "ajax" function that performs can asynchronous web2py connections (see the examples).
<div id="message">Hello World</div>
<script>fade("message",+0.3):</script>
make the message "Hello World" appear. Use -0.3 to make it disappear.
<form><input id="source"/></form>
<button onclick="ajax('test',['source'],'destination');"/>
<div id="destination">...</div>
When the button is cliched an http request to test?source={value of source} is sent to sever and response is placed in destination tag.