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What is Zope 3, and how does it relate to Plone?

There seems to be two different versions of Zope, 2 and 3, which both seem to be under development. I can't install Plone on Zope 3, but need Zope 2. What's up? Should I write my application in Zope 3 instead of Zope 2?

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Zope 3 was originally intended as a ground-up rewrite of Zope, and although it borrowed a lot of experience from Zope 2, it is an entirely separate product. Zope 3 never achieved wide adoption, and never fully supplanted Zope 2.  Instead, many pieces of Zope 3 were incorporated into Zope 2, and Zope 3 itself has evolved into a framework known as BlueBream.  Zope 2 continues to be actively developed, and like BlueBream, it draws on the common set of components provided by the Zope Toolkit.

What does this mean for me?

Zope 3 does not exist anymore.  It is not a "newer version of Zope 2."  Zope 2 is still a live and actively developed project, and is one part of a vibrant Zope ecosystem.  Plone still uses Zope 2, which incorporates many of the technologies and coding techniques that were originally developed for Zope 3.

If you are using Plone, you will be using Zope 2, and do not have to worry about "Zope 3."  You will encounter some pieces of the Zope Toolkit as part of Zope 2.

More background

If you're really interested check out: