Most of us started with D&D / AD&D in one of it's various flavors, although I have seen a significant number that started with other RPGs, which is pretty cool.
This is not a question asking about the RPG that was your gateway into the hobby.
Instead, it's a question about the game that you were drawn to AFTER being introduced to the hobby.
For me, that game was Gamma World. It's not the second RPG that I played (that might have been Gangbusters), but it was the second RPG that I owned and the first one that I bought with my own money. It was also my introduction to the World of TSR "Waxy Dice". What memories. ;)
The Minotaur for Old-School Essentials
*Requirements:* Minimum STR 9, Minimum CON 9
*Prime Requisite:* STR and CON
*Hit Dice:* 1d10
*Maximum Level:* 8
*Armor:* Leather, including shield...