Some of these libraries go a bit deeper. PHPLiveX, for instance, offers an integrated file uploading feature and some intelligent caching to improve performance. A number of libraries take this same approach, and of course some are more integrated with the standard libraries than others. jQuery-PHP is such an option for those who want a plug-in for jQuery.
There are good server-interaction libraries for almost every platform. Direct Web Remoting offers Java stack lovers the chance to call Java code on the server from the client with some security to prevent arbitrary calls. The code also includes a channel for the server to push some information to the clients that are logged in, a useful feature for broadcasting new information.
Blackbird is a stand-alone library that pops up a separate console window that looks quite elegant. You can set four levels of bugs and the user can turn the messages on or off. A profiler is ready to time the routines on the local browser.
Facing the future
Modernizr is mainly a collection of tests that checks to see what features are supported in the current browser. It's a simpler way to take advantage of the new while supporting the old. Most of the tests simply create a DOM object and see whether it accepts the commands.