|works with most smart phones
||app for iPhone and iPad
||app for Android|
Here you can search and browse encyclopedia entries by time period, topic, ethnicity, gender, or keyword.
The Encyclopedia of Arkansas History & Culture (EOA) is a project of the Butler Center for Arkansas Studies at the Central Arkansas Library System (CALS) in Little Rock, Arkansas. As of 2013, the site offers more than 3,200 entries and more than 4,200 pieces of media.
Knovel, the collection of engineering and technical handbooks and manuals, has released an app for Android and iOS (iPads only). My Knovel to Go allows you to save documents from the Knovel database to be read at a later time on your tablet.
How it works:
Wolfram|Alpha isn't exactly an encyclopedia, and it isn't exactly a search engine. The brainchild of Stephen Wolfram, this utilty allows you to compute answers from information gleaned from the web. It is especially useful for measures and conversions, mathematics and computing, and numeric sequences such as population, stock prices, or exchange rates over time.
Wolfram|Alpha is free and you can find the mobile site at http://m.wolframalpha.com/. Definitely bookmark-worthy!