Well, I remember, long time ago, there was SoftICE debugger on Win98SE,
it managed to stop whole windows("Windows OS was in SoftICE's hands, full control, so it could mash windows and press drain button"), so impressive.
But at that time I didn't had an appropriate knowledge to fully operate with it, well I wanted to do some basic memory hacking, like changing score of the game, but SoftICE was too advanced for me. Hehe!