Ask HN: How to learn Ethereum development (for Dapps)?

What would be an interesting Dapp I could write to learn Ethereum beyond the basics? I'm the kind of person that learns better by working on a personal project, but Dapps are totally new for me. I see the potential but not really where to start towards a practical implementation. Do you have any idea what would be an interesting pet project that is not too ambitious, but not too basic? Pointing to existing projects and/or courses is more than welcome! Thanks!