Tacos provides a small set of very functional ajax components. Most of them rely on the dojo javascript library as the basis for their function. Tons of funtionality has been implemented at this point. Effects/refresh/inline editing/validation/etc.
In addition to the core set of components, tacos also provides a fairly comprehensive(growing daily) framework for making any component/tapestry application be able to interact with ajax style requests.
All of the core infrastructure built for ajax integration uses the Hivemind framework to create a dynamic model where interacting with the semantics of ajax requests in your pages is as easy as injecting any other service. Adding support for additional javascript packages is as easy as adding a new configuration point in your hivemind.xml file and providing a class to interact with the library.