Open Source

AxKit
XML Application Server for Apache. Provides on-the-fly conversion from XML to any format, such as HTML, WAP or text using either W3C standard techniques, or custom code. AxKit also uses a built-in Perl interpreter to provide for XML transformation.
http://axkit.org

Enhydra
Java-based application server with XML features, licensed under BSD-like license
http://www.enhydra.org/

GNU-Paperclips
Servlet API 2.1 servlet container. It provides HTTP/1.1 compliance and has an easy to use admin interface. [Open Source, GPL]
http://www.gnu.org/software/paperclips/

The iChilli mobile J2EE platform
Provides a J2EE compliant runtime environment for both server and mobile platforms, such as J2ME, MIDP or other CLDC based devices (e.g. runs on the PersonalJava enabled Sharp Zaurus and Compaq's iPAQ).
http://ichilli.sourceforge.net/

JOnAS (Java Open Application Server)
Distributed platform compliant with the EJB specifications [MPL-like license]
http://wiki.jonas.objectweb.org

maki
XML/XSLT processor utilizing Apache and mod_python.
http://maki.sourceforge.net

ModeliXe
XML-compliant templating solution for PHP
http://modelixe.phpedit.com

MultiXTpm
Contains documentation and information regarding this application server, message oriented middleware and transaction processing monitor. [GNU GPL]
http://www.mitug.co.il/

OpenEJB
Open Source Enterprise Java Beans (EJB) Container System and Server. [BSD-style license]
http://openejb.apache.org/

OpenFrame
Java-based framework for portal applications, providing API's and ready-to-use tools for pages, portlets, user management, content management, collaboration and community services. (LGPL)
http://sourceforge.net/projects/openframe

OpenThought Communications
OpenThought is a Web application engine. Designed to create pages that communicate with web server from DHTML using XML to update portions of page rather than requiring entire page reloads.
http://openthought.net/

PHPAppl - PHP Application Server
PHP-based project geared toward creating web-development environment for non-programmers. Plans to allow web-interface to predefined modules for forums, yellow pages, and news.
http://phpappl.sourceforge.net

Roxen Webserver
Web server and application server which includes support for RXML, a tag-based language for constructing dynamic content. Allows tag plugins to be written in Pike.
http://www.roxen.com/products/webserver/

SkunkWeb
An open source, easily extensible, high performance application server, written in Python.
http://skunkweb.sourceforge.net/

SteelBlue
Open-source Web application server environment in which Web-database applications can be developed completely in an extended HTML language. Similar to ColdFusion.
http://www.steelblue.com/

WebWare for Python
A suite of software components for developing object-oriented, web-based applications. [Open Source, Python license]
http://webware.sourceforge.net/

Whitebeam
An open-source project which provides a complete development environment for web applications using only XML and JavaScript.
http://www.whitebeam.org/

O'Reilly Network: JSP vs. XSP [Feb. 22, 2001]
Sue Spielman looks at JSP and XSP to help you decide which is right for your development needs. <small>(February 22, 2001)</small>
http://www.onjava.com/pub/a/onjava/2001/02/22/jsp_servlets.html