Open Source - Servers
http://www.enhydra.org/
Enhydra Server is an Open Source Java application and webservice server including standard Apache Tomcat (or alternatively Jetty) and Apache Axis with a very big difference ! While the servlet API is used to support presentation logic, the platform contains just about all enterprise level services to build extreme high volume web sites in an n-tier architecture.
http://www.roxen.com/
Roxen WebServer is a full-featured open-source web server distributed under the GPL license. It runs on a number of different operating systems including Windows, Linux, Solaris and Mac OS X.
http://jonas.objectweb.org/
JOnAS is the Open Source implementation by ObjectWeb of the J2EETM specification. JOnAS is a pure JavaTM implementation of this specification that relies on the JDK. JOnAS is part of the ObjectWeb Open Source initiative, which was launched in collaboration with several partners including Bull, the France Telecom R&D division and INRIA.
http://www.webwareforpython.org/
Webware for Python is a suite of Python packages and tools for developing object-oriented, web-based applications. The suite uses well known design patterns and includes a fast Application Server, Servlets, Python Server Pages (PSP), Object-Relational Mapping, Task Scheduling, Session Management, and many other features. Webware is very modular and easily extended.
http://incubator.apache.org/
OpenEJB is an open source, modular, configurable, and extendable EJB Container System and EJB Server.