There's a lot to tell about Plone.
"Plone is a ready-to-run content management system that is built on the powerful and free Zope application server." So says the "What is Plone?" page of the Plone Web site. Wikipedia also has plenty to say.
[Explain what this means.]
Plone.org maintains Wikis, but apparently only to process fault Tickets, that is, as a "bug and feature tracker". There's nothing directly comparable to the Python Wiki.
A PloneSprint is frequently scheduled--half-a-dozen times annually? There are local user group meetings, annual conferences, ...
Plone is particularly prominent in Latin America, Europe, ...