There are five instances of screen-message, configured to use non-standard colors and a fixed-width fonts, and controlled by the rather new remote control feature, where screen-messages repeatedly keeps reading text from standard input until a form feed character (ASCII 0x0C) comes, and displays that. The window manager ratpoison takes care of tiling the instances.
It looks quite a bit like a poor man’s version of dividuum’s great info-beamer. I was told that they also tried out info-beamer, but the Raspberry Pi was too slow and weak for that, while screen-message and ratpoison run happily on such small hardware.
Correction: Info-beamer was not tried, but rather ruled out as overkill for this task.