Open Sesame With Your Source
The trend toward open source software has many benefits when creating applications. JBoss Enterprise Application Platform for example retains the benefits of enterprise application level components such as security and web services without the prohibitive license costs.
Many large companies have gone for the Open source model so it is certainly scalable. In the case of JBoss EAP, the community edition is free and it's the subscription that you pay for. The costs per CPU will increase as your capacity increases, but this will still end up more cost effective than other Java Enterprise offerings. A primary reason for purchasing a subscription is for support as and when you should require it, whether that is during development or for testing, (these phases should be concurrent if you’re using an Agile approach).
Used in conjunction with web application frameworks such as Seam (also developed by JBoss) it provides a solid platform on which to build your web application infrastructure. Seam is continually being developed by Red Hat, and is essentially a framework of frameworks and implements the Model View Controller (MVC) design pattern.
It's not just middle and presentation layer that lends itself to open source. MySQL can be used for the data store component if you're employing MVC. Other object orientated frameworks such as Zend have been used to create a range of applications such as content management systems.
As the old and best clichés tell us though it’s horses for courses. There are a number of obvious reasons such as cost and feasibility which prevent organizations ditching their Microsoft application stack and run into the arms of open source.
Open source providers are also commercially astute so that while frameworks such as Seam may run on Linux, the Windows option is provided for. Scathing as some developers are about Microsoft the financial power it has means that it can invest substantially in R & D. Technologies such as Silverlight will start to come into their own over the next few years as browsers and operating systems that support it become more commonplace, so the challenge to produce innovative, stable and relevant environments is continually laid down to the Open Source community.