PermaWiki is the largest and longest-running wiki devoted to specifically to permaculture. It was founded by Graham Burnett in October 2005. As of late 2015, its content is being ported to Appropedia.
From the PermaWiki main page:
This wiki has been created to facilitate the exchange of information about permaculture, sustainability, environmentalism and organic gardening and farming. We want this to be a resource for permaculture designers, teachers, activists and students as well as anybody who wants to find out more, eventually creating an online, living and growing collaborative Permaculture Designers Manual.