Kiwix is the app for linux.
I want to add a tip for anyone who wants to use it and is running 64 bit system and cannot start the app.
You will know that you need to follow my instructions if the app does not start and you do not get any error messages.
After you download the package from Here!
Open the folder , go to linux folder and then make the file " Kiwix " executable by changing it's permissions to be executed by yourself.
After that , when you try to start it , and nothing happens.
You must install the package ia32-libs.
The above package makes it possible to run 32 bit apps on 64 bit OS.
issue the following command :
sudo apt-get install ia32-libs
Hope that helps as I suffered really till I knew this piece of info and got the app to start and work.