This is a great way to learn all of the notes in both the treble and bass
clefs. You can also practice identifying intervals. The "Lessons" section
is for you to learn new material, the "Trainers" are for you to practice
what you have learned and the "Utilities" are for advanced theory students.
Go explore this link!
Music Theory.net
This link has rotating weekly theory lessons or you can learn about the
history of notation or how to improvise. Explore this link and have fun.
Jazclass