An open source application automates the process of downloading and displaying all of Wikipedia on your desktop, a large task that takes more than a day to complete.
Dubbed Xowa, the software displays an offline copy of 4.4 million Wikipedia articles with full HTML formatting intact. You can even set up additional wikis, like Wiktionary or Wikquote, and navigate between them while offline. For example, you could "Click on 'Look up this word in Wiktionary' and instantly view the page in Wiktionary."
Xowa has been around for a while with support for "Simple Wikipedia," which has just a fraction of the full collaborative dictionary. It was updated yesterday with support for the entire English language-version of Wikipedia.
The SourceForge project page describes:
English Wikipedia has a lot of data. There are 13.9+ million pages with 20.0+ GB of text, as well as 3.7+ million thumbnails.
Setting all this up on your computer will not be a quick process... The import itself will require 80GB of disk space and five hours processing time for the text version. If you want images as well, the numbers increase to 100GB of disk space and 30 hours of processing time. However, when you are done, you will have a complete, recent copy of English Wikipedia with images that can fit on a 128GB SD card.
Although at least 80GB of disk space is used during setup, the wiki files end up being reduced to 25GB after the deletion of a 45GB temporary file and other cleanup.
Besides wiki data dumps and images from the Wikimedia Foundation, Xowa primarily consists of XUL Runner, a Firefox runtime environment; Java; and SWT, the Standard Widget Toolkit for Java.
If you want a download and setup that won't take an entire day, the Xowa developers recommend starting with Simple Wikipedia. "Simple Wikipedia has 184,000 pages and 90,000 images," Xowa writes. "The text version uses 200MB and sets up in five minutes. With images, this expands to 2GB and 30 minutes of downloading time. Simple Wikipedia is a reasonably accurate simulation of English Wikipedia—just much smaller."
Your Xowa-powered offline wiki, simple or not, can run on Windows, Linux, or OS X and can be updated any time from Wikimedia's database backups.