In case you are looking for a Wiki you can integrate into your Portal you will likely search for "JSR 168 Wiki" in Google & Co. This search reveals not much information whether there is a wiki portlet.
Just by luck I discovered that JSPWiki is already integrated as portlet in many Open Source Portal solution: JBoss, Liferay and Sun Glasfish. The status of the integration differs much. While the integration into Liferay is already very good, the integration into JBoss is still Beta2 and lacks attention of the JBoss community. Last friday, JBoss anounced that JBoss wiki will be from now actively maintained by Piergiorgio Lucidi and Luca Stancapiano.
I’m just wondering why there are so many Wiki products out there but no support for integration into a Java Portal which is already a common standard in an enterprise.