Okawix

Okawix lets you download the whole content of Wikipedia, with or without images, so that you can browse it offline:
Okawix is available in 253 languages and includes sister projects of the Wikimedia Foundation (Wikisource, Wiktionary, Wikiquote, Wikibooks).

Okawix is a free software available under GPL licence; sources are available on the SourceForge project.
It's featuring the search engine Wikiwix, developed by Linterweb.

1 Available for free, download the version for your operating system:

Windows Mac OS X GNU/Linux

Educoo + Okawix for Windows

2 Or buy usb keys, filled with an embedded version of Okawix with your prefered content, including images.
This is the prefered solution if you don't have a fast internet access.
Visit our shop.

Questions concerning this software should be asked on our blog

Okawix is distributed under the GPL licence, version 2.