Peter Yared's Musings: Application Servers 2004: A Big Muffin in a Donut World "So perhaps the next generation Application Server is to have NO Application Server in the middle of everything. This is the “donut”, peer-to-peer architecture where there is nothing in the middle, versus the “muffin” architecture, where the Application Server sits in the middle of everything. Anything can talk to anything, and each node has its own mini application server built in so that it can talk to the rest of the world. The interoperability standard is web services, and each of these mini application servers can be written in anything - J2EE, .NET, LAMP, anything that can speak SOAP/HTTP.
Of course for the donut architecture to become fully realized, web services need to become transactional and offer guaranteed delivery."
(Thanks to ChrisH)