openZIM for off line readers, Kiwix has gained a lot of prominence because it is still the only software that uses it.
Functionality to make a selection of articles for off line reading is being developed by PediaPress. This will be done by extending the Collections extension.
The good news is that work is now under way to internationalise Kiwix. This will make it possible for Kiwix to be localised at translatewiki.net.
As the presentation of data in the openZIM format is separate from the data, other off line readers like WikiReader or OkaWix have the option to adopt this format as well. When they do, they will profit from the work by the Wikimedia Foundation as well and when they do there will be a healthy competition for the hearts and minds of our off line readers.