edX.org (https://www.edx.org/) is an amazing web site supported by Harvard University, MIT, University of Texas and other top universities around the world. They offer free online courses on everything from World of Wine from the University of Adelaide to Introduction to Computer Science from Harvard to Introduction to Human Evolution from Wellesley.
For a small fee, you can get a certificate. But, you don’t have to do that. The courses are FREE. Love, love, love this website. And yup, they even have a mobile app too.