What Non-D&D Games Feel Like to Run
Pathfinder
D&D, but more. The systems generally hang together better, if thats a selling feature for you, and the if you like waiting for math to be done, boy is this one going to wow you. It's got more system mastery to demonstrate which is cool, but in general it works like D&D, so you're going to do a bunch of prep work, your players will sidestep it, and you'll scramble to keep laying down track until eventually the campaign fizzles out or you do. Key GM moves are: "PREP" "Study" and "Look stuff up."
OSR
Like D&D, but without all the pesky systems. Most of these run on trust and a steady stream of rulings rather than rules. If your favorite bit of D&D is, "don't worry about it, make something up," the OSR is probably going to be your happy place. Your go-to GM moves are, "say something cool," "refer to a random chart," and "say yes or roll." Less exhausting than D&D, but you're still doing most of the heavy lifting here.
Shadowrun
Watch your friends make complicated characters and then do hours of leg work in hopes of not having to engage overmuch with the combat system. If you've got a Decker, try and keep everyone who is not a Decker engaged as they pull off a solo mission in cyber space. Then do it again as the Mage goes Astral. If you're lucky the plan ends there. If you aren't, you'll probably get to check out the combat rules as the run goes sideways. It's like D&D, but you prep three times as much, roll three times as many dice, shopping trips take even longer, and your party will plan entire sessions to death. Your go to moves here are "wait," "forcibly shift the spotlight" and "look up a rule."
Call of Cthulhu
It's D&D, but you are constructing a mystery. The more they know about it the less able to disentangle it the characters become. There are combat stats and a bestiary despite combat being a fail state. Many such traps exist and you are going to need to tapdance to avoid them. Your go to move is "reveal something spooky; kill a character" and "footstomp a clue."
Savage Worlds
It's D&D, I guess. I mean in a pinch. It's genre-nonspecific and runs on dice pools, but don't let that put you off. The GM is still responsible for cooking up a scenario, awarding experience, and handing out Bennies when the players play their characters according to their Bonds/Ideals/Flaws (okay edges and hindrances, fine) or when they are performing roleplay to your liking. It's fine. It's D&D but you can wear a cool Indiana Jones hat or a jetpack if you want. Go to moves include, "roll, I guess" "make it pulp" and "your performance amuses Caesar"
Powered By the Apocalypse
Despite some early installment weirdness in which one of these is literally D&D, these are not D&D. Prep is minimal, narrative is player-directed, and there's a larger focus on genre and fictional positioning. Fewer rules to memorize, but the way those rules work do <i>not</i> like you fucking with them. Yield to the fiction, hang on loosely. If you play the mechanics, everything falls apart. You've been warned. Your moves are "lean on genre convention" "stir up drama" "feel like you're not calling for enough moves, drastically over-correct and ruin fucking everything."
Forged In the Dark
It's D&D but not remotely. You're a game master for about 30 minutes, and then you are another excited voice in the writer's room. Set up the initial position and then strap the fuck in. This is the only game I've played that will fight you, like full on bottle and chains fight you if you prep. Your go to moves are "build consensus" "ask a question that spurs half an hour of play" and "begin designing a hack."