WebSphere Application Server (WAS) is a software product that performs the role of a web application server. More specifically, it is a software framework and middleware that hosts Java based web applications.
WAS is built using open standards such as Java EE, XML, and Web Services. It is supported on the following platforms: Windows, AIX, Linux, Solaris, IBM i and z/OS.
It works with a number of Web servers including Apache HTTP Server, Netscape Enterprise Server, Microsoft Internet Information Services (IIS), IBM HTTP Server for i5/OS, IBM HTTP Server for z/OS, and IBM HTTP Server for AIX/Linux/Microsoft Windows/Solaris.