Search for the revision that added or deleted the specified text in a Wikipedia article and the user who is to blame. Great for fixing broken references.
Site is a combination of discussion board, blog, wiki, and probably some other things -- includes a huge repository of ebooks in several formats. Of particular interest to Kindle users, the downloadable mobipocket guide is a .mobi format hyperlinked index of all kindle/mobi compatible books.
ProtectEmail is an email obfuscation add-on for PmWiki. It rewrites mailto: links during display into some javascript code which hides the email address.