3 Best AI Alternatives to Khan Academy
Khan Academy is a nonprofit that has helped millions of students learn math, science and humanities, one skill at a time.
Each course is a grid of skills, and every skill moves from Attempted to Familiar, Proficient and Mastered as you practice:

The exercises themselves are short and clear, but they follow the same pattern: watch a video, then solve problems with one right answer:

Here are my favorite alternatives to Khan Academy, starting with the app I created myself.
1. Boterview: The Best AI Alternative to Khan Academy for Any Subject
Khan Academy's main promise is mastery: you keep practicing a skill until you really know it.
Boterview keeps that idea, but it isn't limited to the school curriculum.
Type any topic, or create a course from a PDF of your class notes, and the AI builds a complete course with units and lessons:

I built Boterview based on the idea that passive learning is not the same as learning.
So instead of watching a video first, you learn by answering challenges from the very first lesson.
Some ask you to complete a sentence from memory, which is much harder than picking an answer from a list:

Others ask you to sort or order concepts, so you have to understand how they fit together:

When I make a mistake, the AI tutor explains what I got wrong based on my actual answer, not with a generic hint:

Then spaced-repetition flashcards bring back what I learned right before I forget it:

Want to give boterview's AI a try? Check it out here:
2. Brilliant: The Best Alternative to Khan Academy for Interactive Math
Khan Academy teaches math with videos and exercises. Brilliant skips the video and makes you learn by manipulating things.
In the fractions lesson I tried, I had to color half of a hexagon instead of typing a number:

What I appreciate about Brilliant is how visual it is: you feel the concept before you see the formula.
It also has an AI tutor, Koji, which explains concepts and points you to the right lesson.
The drawback is its scope: Brilliant focuses on math, science and coding, so it won't help with history or literature.
3. IXL: The Best Alternative to Khan Academy for K-12 Practice
If your child uses Khan Academy for extra practice at school, IXL is the other name you will often hear.
It covers pre-K to 12th grade in math, language arts, science, social studies and Spanish, with skill plans aligned to state standards.
Every skill tracks your progress with a SmartScore, so you know when you have really practiced enough:

What I like about IXL is the sheer amount of practice: the fifth grade math page alone lists 392 skills.
The drawback is that it feels more like drills than discovery, which can get repetitive.