Plone development effort happens in two streams:

Plone Core: the living, beating heart of Plone, the Plone Core consists of Plone, Archetypes, and few other packages that are essential to getting Plone up and running.  In order to ensure that Plone's intellectual property remains unencumbered, all contributors to the Plone Core are required to sign the Plone developer's agreement before getting write access to the Plone Core repository. 

Learn more about contributing to the Plone Core

The Plone Collective: a unique, open code repository that contains hundreds of add-on Products for Plone from over 250 developers.  Some of the coolest, most exciting stuff in the world of Plone is happening the Collective, and it's the lab for most of what eventually makes it into the Plone Core.  Access to the Plone Collective is (almost) wide-open. 

Learn more about contributing to the Plone Collective

Please also see the Development section of this website for more in-depth technical information about Plone development practices.