Old RPG You Still Play/Read
I’m going to go with the HERO System, and Champions in particular. Sure, it’s still in print and in its sixth edition, but the core of the game’s component parts have been relatively unchanged since 1981. I’ve owned and played every edition of the game, my favorite iteration being the 4th edition “Big Blue Book.” Plus, I’ve actually GMed really old versions of it in recent memory: 3rd edition Champions and 1st (only) edition Justice Inc. at OwlCon this year. And my Tuesday group still has a 6th edition Champions game on the books we’ll eventually get back to some day.