A super nice member!
I teach ages: 12 to 22
This site features many topics (from K-12 to undergrad math) which are covered in great depth in an alternate way, and doesn’t seem to follow any standard curriculum approach to mathematical learning.
The topics, even if they sound elementary, are often covered in great detail to explore on the theoretical side of thing, with the intention of building a strong foundation in higher mathematics.
For the typical student with average high school level of math proficiency, this site can be slightly challenging, but for others who are interested in exploring mathematics in its entirety (without any dumbing down or otherwise resorting to algorithmic/rote learning), this site could be a hidden gem of the internet.