SoftICE
Ancient? Ughh. I remember using SoftICE to cheat in games back in the 1990’s. Wonderful software, I wish I would’ve been knowledgeable to do something more useful than making myself invincible in Mortal Kombat or giving my characters super powers in UFO: Enemy Unknown (aka: X-Com outside North America).This was a great learning tool to understand how programs actually allocate and use memory. Long before I had taken an architecture class and understood big endian and little endian, I had learned all about it by searching for values in memory. From there you could basically deconstruct the C structs used to handle the memory and then write a pretty simple TSR to cheat the heck out of DOS games. If I recall correctly, at least some of the time I was even able to use it to cheat at APCIDoom - which was a specialized launcher for Doom that let you play four player deathmatches through your local multi-line BBS.