From Foundations of Ajax
Server-Side Frameworks
CPAINT
sourceforge.net/projects/cpaint/
Cross-Platform Asynchronous Interface Toolkit implements Ajax on the server side by returning either text or DOM document objects to the client to be manipulated with JavaScript.
Released under the GPL.
Supports only PHP and ASP.
Sajax
www.modernmethod.com/sajax
Allows you to directly call server-side code from your JavaScript. Sajax supports a number of languages including Perl, Python, Ruby, and ASP (Java is not recently supported).
JSON/JSON-RPC
www.crockford.com/JSON/index.html
JavaScript Object Notation (JSON) is a text format that can be used to exchange data much like XML does. Designed to be easy for humans to read and easy for machines to parse while using conventions familiar to the C family of languages.
JSON-RPC is a remote procedure call (RPC) protocol, like XML-RPC, for the JSON language.
Direct Web Remoting
getahead.ltd.uk/dwr/index
Allow you to call Java methods from JavaScript as if they were local to the browser. Though limited strictly to a Java backend, DWR is one of the more popular frameworks.
DWR fits into common Web frameworks such as Struts and Tapestry and is released under the Apache license.
SWATO
https://swato.dev.java.net/doc/html/
Shift Web Applications TO (SWATO) is another Java-based Ajax framework solution. Work in any Servlet 2.3 or higher container and, like DWR, requires some configuration file updates. Utilize JSON to marshal data between the client and server and allows you to call server-side Java from a browser.
Java BluePrints
www.java.net
The Solutions Catalog includes good documentation on using basic Ajax, implementing autocomplete, creating a progress bar, and validating forms. It also includes JavaServer Faces components.
Ajax.Net
ajax.net
Allow you to call .NET methods from a JavaScript client. Involve a single DLL that can be used with either VB .NET or C#.
Microsoft's Project Atlas
http://atlas.asp.net/Default.aspx?tabid=47
Microsoft is focusing on making things easier for developers by providing a more robust development environment. Microsoft wants to deliver quite a bit, including a client-side scripting framework, ASP.NET controls, and Web Service integration.
Ruby on Rails
www.rubyonrails.org
Allow rapid development of Web-based applications.
While developing Basecamp, the team at 37signals pulled out a framework called Rails.
Basecamp is a prime example of an Ajax application.