There are 3 official apps made by the society and dozens of unofficial apps. Also people study their literature with Apps like Moonreader or Aldiko.
Soon Apps like Moonreader or Aldiko and the other unofficial Apps can be done away with since the JW Library App is updated very often and gets a lot of expanded features and new content.
It wll become the all-in-one App. Soon nobody will need bookbags when they go to the KH. Just a smartphone or tablet will do.