Is there an educational platform like Webassign or OLI that you don't need to be in a class to use and offers upper level and/or grad level math? (Please let me know if I am posting this in the right place, or if there are better tags I could use.)
Is there an educational platform like Webassign or OLI (Open Learning Initiative) that you don't need to be in a class to use?  Also, are there any that offer upper level and/or grad level math?  The first question is more important than the second, but please answer the second if you can.
These platforms give a bunch of multiple choice and/or free response problems.  When you are wrong, some of them tell you what is wrong about your answer without giving away the correct answer.  They also have multiple versions of the same type of question or set of questions to practice with.
So, if you know of any websight or app (fee required or not) that does any of this where you don't need to be in a college class to do the exercises, can you please let me know?
Although, if you know of one where you only have to enroll in a MOOC (Massive Open Online Course), (like EdX, Coursera, Kahn Academy, Udacity, MITOpenCourseware) can you please let me know?
Edit: In case there is any confusion about what types of classes I'm talking about, the most common class that would indicate the level I'm talking about would be abstract algebra (AKA modern algebra). It doesn't necessarily have to include abstract algebra, but it would be the most likely indicator.
The ambiguous ones (as indicators) would be linear algebra, discrete math, and number theory (as these are commonly taught at community colleges, meaning lower division).  But, please share any site that offers these.
There is a long list of (not so ambiguous) upper level (and especially grad level) classes, e.g. modern analysis (AKA real analysis), complex analysis, functional analysis, numerical analysis, numerical linear algebra, differential geometry, algebraic geometry, topology, algebraic topology, differential topology, logic, set theory, combinatorics, graph theory, probability theory, and I'll just include category theory for the sake of wishful thinking
 A: I would reccomend you register for MathXL under self-study.
A wide array of Pearson published Math textbooks have MathXL content.
This includes textbooks for post-secondary level courses up to Differential Equations and Linear Algebra. No higher level courses, unfortunately.
You can register here: https://www.pearsonmylabandmastering.com/northamerica/mathxl/students/get-registered/index.html
You will have to pay for access though. Just like enrolled students need to beyond a trial period.
I personally find MathXL far more comprehensive than WebAssign and am using it for self-study while taking Calculus II.
Another reccomendation is Zybooks online textbooks, if you are looking for an online interactive textbook. However they do not provide a drill evironment like MathXL. Again nothing for higher level courses.
https://www.zybooks.com/
Edit:
I thought you might be interested in reasorces for the basic set of undergraduate math courses (Calculus I-III + Differential Equations and Linear Algebra). If you want similar reasouces beyond that level I have no idea.
