As the world has moved towards the cloud/Internet so has the need for applications designed to manage them. Among these are so called, 'Application Servers' which serve to manage web based applications. Often, they are/run language/platform specific applications and are able to significantly manage the environment in which the application operates. In most modern and competitive environments you're able to achieve fine grained control of security, the amount of memory available to a particular application, the number of threads that are available to an application at any one time, and increasingly, application level load balancing/redundancy. In fact, in some of the more advanced application servers its almost like having a virtual server.