Here are five:
1. Cooking classes. Check out the BBC and "The New York Times" for free recipes and how-to videos. TheKitchn.com is another good one.
2. Learn an instrument. Fender has free guitar, ukulele, and bass classes for the next three months. They offered it to the first 100,000 subscribers, then extended it the first ONE MILLION people who sign up at Fender.com/PlayThrough.
3. Learn a new language. If you're a student or have kids, Rosetta Stone is offering three months of free online classes.
4. Learn to code. You can start learning the basics at FreeCodeCamp.org.
5. Take a free Ivy League course. ClassCentral.com has a list of 450 online classes you can take. Everything from nursing to quantum mechanics.