Yes, but I haven't used any so can't recommend one
Dojo is the only one that springs to mind (and I think Ajax is just part of their kit IIRC). Mentioned on this [link|http://www.ajaxian.com/|Ajax blog], which probably has other pointers.
Bah. Now I'm fifteen minutes late for work again. Why does responding to posts take so much longer than reading them? ;)
The Sig:
"Despite the seemingly endless necessity for doing so, it's actually not possible to reverse-engineer intended invariants from staring at thousands of lines of code (not in C, and not in Python code either)."