7 Best Free Application Servers

An application server is computer software which provides the business logic for an application program. It offers services such as management of large distributed systems, data services, load balancing, transaction support, and network security. The application server is one part of a three-tier application, consisting of a graphical interface server, an application (business logic) server, and a database / transaction server. Many application servers support the Java platform, but they can be found in other environments.
There are good reasons to deploy an application server in a corporate environment. At a high level, an application server enables updates and upgrades to applications to be distributed to all users. System administrators also benefit from the fact that changes to application configuration can take place centrally, which greatly simplifies technical support and ultimately the end user experience. Application servers also simplify user management, avoiding the need to set up and maintain user-management systems for applications. This type of software also enhances scalability and resource usage, and exposes business components via different deployment wrappers.
As the cloud becomes increasingly more important, the role of application servers is only set to increase.
To provide an insight into the quality of software that is available, we have compiled a list of 7 application servers which may result in significant cost savings for organisations which develop enterprise applications.
Two software applications which are worthy of a mention are IBM WebSphere Application Server and Apache Tomcat. IBM's offering is available in a community edition that is released under a free to use and distribute license, but it is based on Apache Geronimo which is featured below. Apache Tomcat is, in fact, a web container not a fully fledged application server. A web container is the web component of a web server that interacts with the servlets, Java classes that extend the capabilities of servers that host applications access. Nevertheless, Tomcat avoids some of the overhead associated with full-featured application servers.
To provide an insight into the quality of software that is available, we have compiled a list of 7 impressive open source application servers. Hopefully, there will be something of interest here for any organisation that wants a layered architecture.
Now, let's explore the 7 application servers at hand. For each title we have compiled its own portal page, a full description with an in-depth analysis of its features, together with links to relevant resources and reviews.

Application Servers
JBoss	J2EE platform for developing and deploying enterprise Java applications
Zope	Object-oriented web application server written in Python
Apache Geronimo	Create Java/OSGi server runtimes that meet the needs of enterprise developers
GlassFish	Provides a structured process for developing an application server
Zend Server CE	Web application server for PHP 5
JOnAS	Implementation of the Java EE 5 certified application server specification
Jetty	HTTP Servlet Server (Application Server) written in Java