There's a comment on HN that says that Gnus includes code written in elisp bytecode. That's amazing if so (I can't find it in a brief read).
miniblog.
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WebAssembly seems like a totally reasonable bytecode format, but I've not had many opportunities to use it so far.
Has wasm found its 'killer app' yet?
On storing ASTs in flat arrays for performance, and the relationship with bytecode interpreters:
Bytecode interpreters vs tree walkers, and beating GNU Awk performance in GoAWK: