It's a javascript-based imitation, much like all of those js-based imitations of various Windows versions.

The original source code isn't really involved, which is a shame, since it is actually available.

IMHO this should have been (something along the lines of) GNUstep + TimBL's original code (mirror: https://github.com/cynthia/WorldWideWeb) + Emscripten + getting Emscripten to work with ObjC. Now, that would have been cool.

This is the most commented HN posting on this from that time (2019):

https://news.ycombinator.com/item?id=19249373

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nine_k 7 hours ago | parent | next [-]

A WASM emulator of 68040 and NeXT, the original OS and compiler, then run WWW on top of that.

The performance would likely be comparable %)

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actionfromafar 6 hours ago | parent [-]

The performance would likely be much better. :-)

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lysace 6 hours ago | parent [-]

An example from a year later; 1990:

https://copy.sh/v86/?profile=windows30

	▲	spijdar 6 hours ago \| parent [-]
		Every version of NeXT is actually catalogued and can be run in the browser at: https://infinitemac.org/ I'm pretty sure the CERN WorldWideWeb application is also included in the "bonus software" HDD, but I'm on my phone right now and can't confirm. :-)

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krackers 6 hours ago | parent | prev [-]

You can already run nextstep in browser, see https://aresluna.org/frame-of-preference/ (section "Back to 1992")