[Turhan's Bey Company]

That wiki page isn't a bad introduction. It's a movement of mostly older gamers which uses older--like, pre-AD&D--editions of D&D and similar very early RPGs as inspiration. There are a number of OSR products on the market produced in deliberate emulation of those old games in structure, content, and appearance. Relatively rules light ("Rulings rather than rules" is a common motto), mostly about killing things and taking their stuff rather than more complex plots, but on purpose this time rather than operating in the framework of pioneering an entirely new genre of gaming in the 70s when none of us really knew what we were doing. It strikes me as being somewhere between nostalgia and an attempt to create what us older gamers now like to think we could have experienced back then.