Kiwix

NOTE: This version might not be able to read newer ZIM files.

Kiwix lets you read Wikipedia and other websites without an Internet connection.
It uses the highly compressed ZIM format to store
webpages for quick and easy reading.

The app is a lightweight piece of software reading bigger files stored on your
device or SD card: once it is installed, you can select which additional content
you would like to download (Wikipedia, Wiktionary, TED talks, etc.) and be ready
for when your internet connection is bad (or need to be in airplane mode)!

Note: Kiwix is also available on regular computers (Windows, Mac, Linux).