YouTube

Whether you want to learn more about math, history, or wildlife, there’s a YouTube channel out there that probably already has hundreds of hours worth of content for you to dive into.

Of course, that isn’t always the best case scenario, especially for people who don’t know much about a topic. You’ll probably need to dig a little bit to find the best, most useful videos. But the good news is that you can check what the comments say to make sure other people like and agree with the content creator. 

Granted, YouTube might not be the best if you’re looking to get a structured course or a certificate to add to your resume. But if you want to work on a weak subject, or just learn because you like learning, this will be a great platform for you, as everything is free (so long as you can stand all the ads).