Discuss over coffee: Building an enterprise application stack using open source

I want to share my experience in building a completely scalable stack using open source software, starting withe CentOS all the way through Ext-JS on the front end. And I would like to hear from others where in their stack they are using open source.

You will hear about: CentOS, PostgreSQL, Sun MQ, Glassfish, DWR, Ext-JS etc. And why we chose the software that we chose. Feel free to share your experience.