EDIT: I’ve updated the list below with Broomstix.
Unfortunately, there is no official Harry Potter RPG. Rumor is it that that JK Rowling isn’t a fan of the idea of players creating their own stories within her universe. Be that as it may, players have been desperate to play in the HP universe. There have been a ton of adaptions, including on my part. You can see a ton of different options below, split into those which are explicitly unauthorized adaptations of Harry Potter, and those which aren’t explicit, but imply a Harry Potter-esque setting, which you can use in the Wizarding World. I’m including my Fiasco playset, my Risus adaptation, and my Bubblegumshoe adaptation here.
Harry Potter RPGs
Risus Hogwarts: Back in 2005, I adapted Risus over to Harry Potter, but didn’t get it up on the site here until 2016, having found it while scrounging around in the basement of my Google Drive. It’s simple, ready to run. Take 2 minutes to make your character, and run with it!
Bubblegumshoe Harry Potter: Another adaptation I made, more recently, which has gotten a lot of views. People seem to like it. Take Bubblegumshoe, throw in some wizards, and BOOM! You’ve got a whole game based in Hogwarts.
CODA System Harry Potter Core Rulebook: The CODA System, which was used for the most recent previous version of Star Trek as well as the Lord of the Rings movie RPG, has been adapted over into a Harry Potter RPG. The CODA system is similar to the D20 System, but it uses d6s instead of D20s.
Broomstix: Created by Momento Mori Theatricks, the guys behind InSpectres and Freemarket and Parsley Games. I remember checking this out while on deployment in 2007. It’s a nifty, light little system.
Wizarding School RPGs
Toil & Trouble: My Fiasco playset, designed for playing as magical wizards at a magical school. I’ve seen a lot of people play this online and love it. Enjoy! And let me know how your game goes!
School Daze: Roleplaying the angst of being a high schooler, by my friend Tracy Barnett and illustrated by D20Monkey’s Brian Patterson. Page 50 of the core rulebook features how to run your high school at a magical wizarding school. It’s a good one!
Eldritch High: An RPG set in Alexander Circe’s Academy for the Study of the Esoteric and Eldritch Arts. Not gotten a chance to look at this at all, but it’s by John Wick (No, not that one), who’s a great game designer.
Witch Girls: Witch Girls is a fantastic and beautifully illustrated game by Malcolm Harris. It’s been out for a while, but apparently, he kind of screwed his backers and ghosted them on Kickstarter for the 2nd edition, so fair warning, if you don’t want to back people who haven’t talked to their backers in two years. I didn’t back the KS, but know some who did.
Any more I should add to the list? Let me know!