This ZopeProduct may be used to enable wiki-linking in the text fields of (new) Archetypes content types in Plone sites. "Wicked provides a site-wide type agnostic wiki linking and content creation as a drop-in replacement for the Archetypes TextField."
Wicked is built in to Plone 3.0. You must activate it in site setup -> markup -> wiki behavior, then you can use '((page name))' in Pages like wiki links.
See http://zwiki.org/PloneAndCMF#zwiki-and-wicked for a comparison with ZWiki.
http://plone.org/products/wicked -- home