Etude

Built an interactive coding-practice app: 802 lessons across 28 language and topic tracks, from novice to expert. Learners read a concept, write code in an in-browser editor, and run it against real tests, with Python running in WebAssembly and JavaScript in a Web Worker, so code execution costs nothing server-side. A verification script confirms every lesson's reference solution passes its own tests before release. Includes account sign-in on a Fastify backend and installs to a phone home screen as a progressive web app.