Earlier quoted context omitted.
So I could write an application in, lets say Rust, compile it to WASM and run it on Linux, macOS and Windows browsers without anything extra?
Yep! It's a completely portable target and fulfils the promise of “compile once, run anywhere”, although how well it runs depends on the particular browser. (It is pretty amazing you can compile C code to something that actually runs on multiple machines, it's very nice.)
Can this be used as alternative to native modules in Node.js?