Exercism
exercism.org
Practice exercises in 80-odd languages with free feedback from a human mentor
exercism.org
Practice exercises in 80-odd languages with free feedback from a human mentor
khanacademy.org
Explains school maths and science one short video and one exercise at a time
metronomeonline.com
A metronome that starts clicking the moment the page loads
monkeytype.com
A typing test you can tune to the exact words, punctuation and length you want
musictheory.net
Free lessons and endless drills for notation, intervals, chords and ear training
yoodli.ai
Records you answering a question and counts the filler words back
Cuts across
A tag is orthogonal to the category tree — that is what makes it worth having.