Best free online courses you've taken (and completed)?

I just finished The Science of Well-Being on Coursera, and I loved it! Taught by a Yale Professor, this course is all about the psychology of happiness and well-being. What I loved about this course is how it challenges common misconceptions about happiness and provides science-backed insights into what really makes us feel fulfilled. IWhat other free online courses have touched your life? I’d love to hear your recommendations!