CS50 — Harvard's Introduction to Computer Science

The most popular university course in the world, taught by David Malan with theatrical energy that makes algorithms feel like a TED Talk. CS50 covers C, Python, SQL, HTML/CSS/JavaScript, and algorithms — the same material Harvard freshmen pay $60,000/year to access. Available free on edX with 4 million+ enrollments. The problem sets are famously challenging (the "ducky" debugging tradition is iconic), and the community Discord has 100,000+ members helping each other. Completing CS50 is equivalent to a semester of university CS and is recognized by employers. The certificate costs $149 but the content is 100% free.