A forgotten one is webassembly.studio, an in-browser IDE for creating WASM projects with way less pain than other methods. It got discontinued the year I needed it for my school project. It was open source but I failed to rehost it myself and public mirrors only appeared after I spent days trying to make Emscripten work, tore my hair out over WebGL and then finally painfully built the whole thing with CSS (and a bit of JS; yes, it was indeed a disaster).