In yet another ‘probably-useless-but-interesting’ hobby project, I wrote a Forth compiler and interpreter targeting WebAssembly. It's written entirely in WebAssembly, and comes with a compiler that dynamically emits WebAssembly code on the fly. The entire system (including 80% of all core words) fits into a 10k (5k gzipped) WebAssembly module. You can try it out here, or grab the code from GitHub.
What follows are some notes on the design, and some initial crude speed benchmarks.