My favourite was Casio PocketViewer PV-S660 I used during high school as calculator, for note taking, learning programming and playing games. You could not do m

My favourite was Casio PocketViewer PV-S660 I used during high school as calculator, for note taking, learning programming and playing games. You could not do much on 6MB flash and 160x160px monochrome display, but it was awesome device for the time. On two AAA batteries it lasted for months of everyday use (without backlight).