Special:CategoryTree – can generate a tree of categories, or categories and articles
User:Chris G Bot 2 – produces, for a given category, a table listing all articles within that category (and all subcategories of that category), and the status of those articles (a clone of User:PockBot, which is disabled)
CatScan - a tool that can do various types of category scans, including intersection (may or may not be using up-to-date version of database); can search subcategories
Wikipedia:Wikimedia Commons – has over three million media files (photographs, diagrams, animations, music, spoken text, video clips, etc.) available for use in any Wikimedia (community) project, to which anyone can contribute; recommended place to upload free images to, rather than to Wikipedia
User:MonoBot – fixes (some) problems when an or doesn't do a move to Commons totally correctly
Duplicate images – tool to show duplicate files between Wikipedia and Commons
Push-for-commons – tool to show a set of images from a wikipedia, helping to find license problems, {{NowCommons}} candidates, and images that should be copied/moved to the commons.
WikiLook – Firefox add-on that provides Wiktionary information about any word on a screen, when specially selected (shift or highlight plus mouse move)
Wikipedia:External peer review – information on formal and informal reviews of the overall quality of Wikipedia articles, done by outside experts, not initiated within Wikipedia
GeoPedia – provides iPhone owners with a Wikipedia feed customized to their current location
mw:Beta Features/Nearby Pages - Adds a button to the top right corner of pages that contain geographical information, to get the reader to "nearby" pages
Monthly chart for any specified page ("Wikipedia article traffic statistics") (for pages that are not articles, include the namespace as a prefix) ("Hendrik's tool")
tools:~emw/wikistats/ - Wikipedia article traffic statistics (alpha, as of November 2013)
Special:Random (in the standard navigation box on the left) (adding a suffix – /Category, /Help, /Image, /Portal, /Template, /User, or /Wikipedia) will take you to a random page in those namespaces)
User:Zocky/Auto Complete – auto-completes the titles of articles in the search box (JavaScript) (no longer required as of May 2008; this is built into the search function now)
Robots.txt file – specifies search engines that are not allowed to crawl all or part of Wikipedia, as well as pages/namespaces that are not to be indexed by any search engine
Wikipedia:Request an account – for those who wish to create an account but cannot read the CAPTCHA image that is part of the standard registration process as of February 2007