ARSCIF is a powerful framework that makes it trivial to use asynchronous remote-script callback invocation (AJAX) techniques. It helps the developer by working out problems such as data and character encoding, concurrency control, browser implementations, and so on, allowing the creation of pages with sophisticated, dynamic features.
Address Book Continued is a multi-user address book Web application. It also makes use of AJAX, which means that page reloads only happen on login/logout; the rest of the operations is handled asynchronously in the background. It's well usable, even over slow connections. You can even install ABC on your desktop PC and configure it so that it doesn't require login for connections coming from the local computer.
Aranha is a piece of software written to allow Web applications to be written more cleanly and more easily. It is a Local FastCGI Responder, although work is in progress to allow it to work as a FastCGI Authoriser and a FastCGI Filter. It is based on the programming language Lua, and contains many extensions to enable easy Web site development and maintenance.
The Atom Publishing Protocol framework for Ruby aims to simplify the implementation of Atom Publishing Protocol (APP) support in Web applications. It achieves this by implementing a framework that handles the protocol-level duties for the programmer, while not making any requirements for the site design.