Warren's Dark Heresy Game
Like a 40k tablet computer, except its only functions are:
send and receive email, pictures, including attached sound and video
Messages take about a day to send, planetwide, and are notoriously full of static and blips. But the instance of dataslate corruption by heretics and traitors is next to zero, and data-slates are almost as cheap as paper to make. Typically only the clergy can read them, however…
Note that each message contains an automatically-generated “inspirational” Emperor message which is impossible to delete.