Powers of Minus Ten, and yes it still exists - I do a little bit of maintenance to keep it alive because it's used by a bunch of schools. https://apps.apple.com/us/app/powers-of-minus-ten/id42912355...

I'm actually still working on something similar but, basically, no longer trying to run a business selling educational games (more, profits from commercial development contracts with actual budgets funding the cooler projects).