I've recently worked my way through high school math and am about to complete the linear algebra course (https://www.khanacademy.org/math/linear-algebra).
I've done most of the stuff on the precalculus playlist (not all on khan, some by books) - https://www.khanacademy.org/math/precalculus.
I struggle a bit finding the next playlist. It's obviously calculus, but there are a lot of playlist which seem to cover the same stuff:
There is "AP Calculus AB" and "BC" and I get that BC is AB + more stuff.
But there is as well "Differential Calculus" and "Integral Calculus" and "Differential Equations" and lots of other playlist and most of them have roughly but not exactly the same content.
What's the purpose of that and where do I continue?
Are there other online learning systems to recommend (I'm willing to pay and am not interested in a formal degree).
Edit: There is as well https://www.khanacademy.org/math/calculus-home, which looks like it covers everything.
http://tutorial.math.lamar.edu
I highly recommend you to follow Paul's Math Notes, which contains everything from Algebra to Calculus III. His notes are highly readable, nicely organized, and filled with great examples.
For additional practice, I recommend Thomas' Calculus or Stewart Calculus.