Another good books with a critic view on gamification:
Rethink Gamification - Edited by Mathias Fuchs, Sonia Fizek, and Paolo Ruffino
Gameful World - Edited by Steffen P. Walz, and Sebastian Deterding
It’s not one of your options, but you should check out the Gamify your Life Notion template. I have been using it for about 4 months and I have been enjoying the flexibility that it allows.
I highly recommend that you check out #theGamificationProject, which is a combination of Notion templates built for gamification.
You can use it to create a family dashboard that includes a leaderboard. Everyone in your family can have an avatar and level up by completing tasks and habits.
You can also create a whole theme. Since I’m a developer, I chose to create a theme that’s based on Transistor, which is a game by Super Giant Games.
It actually launched on Product Hunt today. Here’s the link:
You should consider making a character whose skills improve as you level up: e.g. whenever you complete a work out, add some points to something like "Strength."
You could draw a character that suits your taste as in this app I've been using that lets you customise your look, for example.
I don't know if this is exactly what you're looking for, but if the class requires a digital/programmed component you might find Twinery useful. It's great for if you want to program a simple text-based game. It can do some pretty cool things and is easy to use.
If the class is more on the gamification process, I'd suggest going more analog with something like custom item cards, leaderboards, or sticker badges. There are websites for making all those things if you're not feeling super artsy yourself. I use MTG Cardsmith myself to make item cards for my gamified English class, but you can get pretty good results in something like Google Slides as well.
There's a cool text-based game platform that's very easy to use, but also super powerful. It's called Twinery. It's completely free and might fit your needs.
Edit: I've actually had my 9th grade English students use it themselves to create digital choose-your-own-adventure games.
I maintain a personal "skill tree" of sorts to track things I'm looking to learn and their relative milestones and daily targets.
Thanks for the Habitica suggestion. I'll try running it all through that.
Even Ninja Monkeys like to Play is a good introductory book.