WebSphere Application Server is described as 'provides the availability and security your business depends on while optimizing cost' and is an app in the Development category. There are eight alternatives to WebSphere Application Server for a variety of platforms, including Mac, Windows, Linux, Self-Hosted solutions and PHP. The best alternative is JBoss, which is both free and Open Source. Other great apps like WebSphere Application Server are Glassfish (Free, Open Source), Oracle Weblogic Server (Free Personal), appserver.io (Free, Open Source) and Apache Geronimo (Free, Open Source).
JBoss is Red Hats Java EE 5-compliant (soon Java EE 6-compliant) application server. It is, as with Red Hat itself, dual-licensed either as open source (community edition) or commercially (enterprise edition).
GlassFish v3, built by the GlassFish community, is the first compatible implementation of the Java EE 6 platform specification. Many of the Java EE 6 themes carry over to Sun GlassFish Enterprise Server v3 - flexibility, extensibility, and developer ease of use.
appserver.io is a multithreaded application server for php written in php. Our technology allows real multi-threading in PHP and different useful services for developers enabling more efficiency and security. And best of all – it is completely open source!
JOnAS is a leading edge Java EE 5 certified Open Source OSGi Enterprise Server by OW2. The License used by JOnAS is the LGPL. The OW2 development community includes many academic institutes (Grenoble University, INRIA, LIFL, Peking University, UPM, ...