An application server is a piece of software designed to help make it easier for developers to isolate the business logic in their systems architecture (usually through components) and develop three-tier or n-tier applications. Typically application servers also offer additional features such as transaction management, clustering and fail-over, and load balancing.
Zope (the Z Object Publishing Environment) is an Object-Oriented, Open-Source Application Server and Content Management System. It is written in Python, itself an open source language, and is based on the Bobo Object-Request-Broker and the Principia content management system.
Please add only English websites related to Plone. You can add Plone solution provider here http://dmoz.org/Computers/Software/Internet/Servers/Application/Zope/Solution_Providers/