Third, lets you introduce as few keys as possible to the lesson, adding more keys automatically when it decides that you are proficient at the current level. When you only start learning it generates lessons with words from a very small alphabet of the most frequent letters. When your typing speed for every key in that alphabet reaches certain threshold, the algorithm adds the next most frequent letter to the alphabet. And so on, until the next letter. This way you will learn the most frequent letters first, and the least frequent ones later. 

Scott Morris is Skillcrush's staff writer and content producer. Like all the members of Skillcrush's team, he works remotely (in his case from Napa, CA). He believes that content that's worth reading (and that your audience can find!) creates brands that people follow. He's experienced writing on topics including jobs and technology, digital marketing, career pivots, gender equity, parenting, and popular culture. Before starting his career as a writer and content marketer, he spent 10 years as a full-time parent to his daughters Veronica and Athena.
Spend an afternoon brushing up on statistics. Discover how the Krebs cycle works. Learn about the fundamentals of music notation. Get a head start on next semester's geometry fundamentals. Prepare for the SAT, GMAT, LSAT, MCAT, NCLEX-RN, and AP exams. Or, if you're feeling particularly adventurous, learn how fire-stick farming changes the landscape of Australia.

EdX is another leading online-learning platform that is open source instead of for-profit. It was founded by Harvard University and MIT in 2012, so you know that you’ll learn about cutting-edge technologies and theories. Today, edX includes 53 schools. You probably can’t go wrong with the free Introduction to Computer Science from Harvard University.