Wikitaxi allows you to "take Wikipedia with you while you are offline."
It's an interesting application, if you rely on Wikipedia. I have given up on it, however, because of the heavy-handed practices of subject editors.
Just take a look at this and the following note: "The topic of this article may not meet the general notability guideline. Please help to establish notability by adding reliable, secondary sources about the topic. If notability cannot be established, the article is likely to be merged, redirected, or deleted. (May 2010)."