Udacity

Udacity hosts over 200 free courses in programming, data science, AI, and cloud technologies, created in partnership with industry leaders like Google and Amazon. Each course includes video lessons, quizzes, and projects. The free tier provides full access to individual courses; nanodegrees and professional certificates carry a subscription fee.

Good for learners exploring new tech domains before committing to paid certification, or for those supplementing other learning. The breadth of free content makes it a useful reference even if you don't pursue paid credentials.