Khan Academy

khanacademy.org

article-format वाले lessons सीधे import होते हैं; video lessons उनके YouTube वर्शन के जरिए आते हैं।

Its article-format lessons import cleanly on their own, while video lessons need the YouTube route since the site itself doesn't host a transcript. That combination makes it a solid base for a beginner-level study notebook in math or science, K-12 through early college. Depth stops well short of college-level rigor, so it's the wrong source once a notebook needs to go past the fundamentals.