The source code for WorldWideWeb is available: https://github.com/cynthia/WorldWideWeb. I've got it in the back of my mind to try to get it building at some point (either in Previous, or on real hardware; I have a few working NeXT machines).

As an ObjC programmer who started 15 years after it was written, it's interesting to see how different it is from even NeXTStep 4.2 (aka OpenStep) era code. Most methods don't have explicit return types (still valid, but ~never used), lots more C, no Foundation (didn't exist yet), AppKit was still using NX, etc.

That said, you can tell it's fundamentally the same toolset. There are still classes that more or less exist and work the same way today on modern Mac OS versions, it uses a NIB file, etc.