I would love to see a wasm repl online. Something that's focused on teaching the language, not for people who are going to write compilers that target it, but for people who are confused about what it is and how it works, as a way of demystifying wasm so that they have more confidence in choosing to adopt it. Maybe something that really visualizes the ins and outs of a wasm program, and maybe some kind of dynamic visualization of how the s-expressions transform into stack-based code. Just an idea, but I think it could be useful and fun for someone to make for those of us who want to play around with wasm without installing anything :)