Copies of Wikipedia content
OpenFacts, the Open Source Knowledge Database
When Wikipedia is down, you can find many articles from the following sources. Links given here are to the main page and to the Current events page, to see how up-to-date the contents are.
All language versions
English, Simple English and French version
As of June 2007, the most up-to-date are:
Also fairly up-to-date (some more than a month old):
Not so up-date:
- WordIQ 
- the "definition" tab has the Wikipedia content
- has also images with image pages (but only those on Wikipedia itself, not those on Commons), e.g. ; for all images there is a local copy, including the full version of large images, e.g. 
- has also category pages, e.g.  but members of the category do not show or link to the categories they are in
- shows also templates, e.g. , but, as for other pages, not the wikitext
- http://www.nationmaster.com/  to get e.g. the article Train station, use http://www.nationmaster.com/encyclopedia/Train-station, with a dash or an underscore for the space; has also image pages, e.g. http://www.nationmaster.com/encyclopedia/Image:Fuji-apple.jpg . However, there is a local copy for the images in articles, in that size, only, the image pages embed/link to the images on Wikimedia.
- http://www.mcfly.org/en/  - no images (neither local ones, nor links to Wikimedia)
- Open Encyclopedia  Uses multilingual branches of Wikipedia for most of its articles, provides cached article images.
- Hall Encyclopedia Free online encyclopedia, dictionaries, quotes, sources, news, and pictures. Many articles in differents topics and provide links to related sites.
- Freepedia  - English version of Freepedia
- explanationGuide [current events page is missing] - with pictures
- Asinah.NET [current events page is missing]
- 4Reference cache  - listed in alphabetical order. Not updated often; there are strange omissions, e.g. articles with titles starting with "trai".
- Fact-Index  - pretty much straight copy of a lot of Wikipedia material, plus Google ads.
- http://www.logicjungle.com/wiki.php [current events page is missing] - with pictures. Search doesn't work.
- http://www.tutorgig.com/encyclopedia/  - to get e.g. the article Train station, use http://www.tutorgig.com/encyclopedia/getdefn.jsp?query=train_station ; for a full text search put "train station" (with the quotation marks) in the search box (this corresponds to http://www.tutorgig.com/encyclopedia/sencyclo.jsp?query=%22train+station%22 ); this does not put an article with a matching title at the top (in fact, in this case the article "Train station" is at position 41!).
- http://www.phatnav.com/ 
- http://www.encyclopedia4u.com/ 
- http://encyclopedia.thefreedictionary.com/ [current events page is missing] - When pointing at a link, the first part of the linked article pops up (applies for a limited number of links per article); if you double-click on a word, it looks it up in a dictionary; at the bottom of each article is a list of alphabetically preceding and following encyclopedia and dictionary articles; when following an external link it is automatically opened in a new window.
- http://answers.com/ [current events page is missing] - search engine that returns cached versions of Wikipedia content (as well as a few other sites) - has image pages with copies of images, and allows searching in the titles: 
- http://www.book-spot.co.uk/  - has also the wikitext, e.g. http://www.book-spot.co.uk/index.php?title=Train&action;=edit
- http://www.penguin-directory.com/ - a fork, but edited so infrequently (as of 24 Feb 2005) that it is essentially a copy dating from Sept 2004, but with the benefit of features such as "What links here".
- has also image pages with a local copy of the full version of the image, e.g. 
- http://www.encyclopedia-online.info/Main_Page - ditto, copy from Aug 2004, but images in the articles only, not on the image pages or category pages.
Not yet checked on being up-to-date:
The first part (ca. 230 characters, sometimes less) of basically each article, linked to the full current article, can be found on:
- http://lexikon.izynews.de/ (max. 2 weeks old)
Nederlandstalige versie (Dutch)
- http://encyclopedie.izynews.be/ (max. 2 weeks old)
A cached copy need not be the latest version, of course.
Sites that show when a page was updated:
Also the Current Events article may give an indication of how recent the cached copy is (although it is possible that this page is more frequently refreshed than other pages), see the links above.
For OneLook see http://www.onelook.com/?d=wik
PhatNav has its own copy of all images. NationMaster and OneLook have no images, 4reference and TutorGig have some. In each case image captions are shown anyway. Onelook shows alternate text, TutorGig also "No image" with the file name. Except in the latter case the result may be somewhat confusing. Google and t-st load images from the Wikipedia server, so they are not shown when that is down. Google has a separate cache for images (small versions only), so one can do a separate search for the image.
For TeX the code is shown, not the rendered image, except in the case of Google (see Images).
Only Google and PhatNav have pages in all namespaces, the others have pages in the main namespace only. Apparently accidentally, some pages in other namespaces are included: some Talk pages, and some User and User Talk pages in the case that there is also an article with the same name. They have titles without "Talk:", etc., and are there at the expense of the article itself; e.g., compare  with .
The image description pages in PhatNav wrongly mention "There are no pages that link to this image." and do not link to the image itself.
Phatnav includes the editable parts of categories, but even Phatnav does not show the pages a category contains, while pages do not show to which categories they belong.
Google, TutorGig, PhatNav and explanation-Guide allow full-text searching. NationMaster also, but it does not give the page with the search term itself as title!
PhatNav allows specifying the namespaces to be searched, but this and specifying the requested number of search results reset each other, therefore one can better use the URL: to search all namespaces use  with "xxx" in the URL replaced by the search term.
Note that finding a phrase on TheFreeDictionary with Google is affected by the pop-ups: these texts are considered to be inserted in the main text. Thus one finds a page which just links to the page one is looking for (if the search text is in the beginning of the article, hence in its pop-up text), but not an article whose own text contains the search phrase, but with e.g. the first word being a link (due the inserted pop-up text there is no match).
Internal Wikipedia links
In a page cached by Google, the link is to the original Wikipedia page and can therefore not be directly used when Wikipedia is down (to get the cached copy of the linked page, check its title and do a new search for it); OneLook has no links; for the others, the link is to the cached copy of the other page and can therefore be used directly.
External links work in all cases.
4reference and t-st do not contain redirect pages; links to redirect pages have been removed. In NationMaster redirects work; the page to which is redirected gets the title of the redirect page, and there is no message about the redirect. This may be confusing when the redirect is not to a synonym but a related term. In TutorGig and OneLook redirects work also, and the page to which is redirected shows its own title. The message "Redirected from ... " is never shown.
The caches do not contain page histories.
"What links here"
Google can give web pages (not necessarily all) linking to a given web page, hence also those linking to a Wikipedia page. These are often also Wikipedia pages, but there may also be external ones.
Copy of Wiktionary
- Open Dictionary Uses Wiktionary for most of its articles.