Model 95 users who run OS/2 will know that there is an option to use the information panel on the front of the machine as a kind of 'disk activity light'. The rightmost position of the character display appears as a pulsed lighted block, making up for the lack of a disk activity light on the machine itself.
DLITEDOS is a device driver for providing the same functionality under DOS. It is not fancy; all it does is show the same pulsing block that OS/2 does. It has the advantage of being very small, and not taking up much precious (under DOS, anyway) memory.