This is Mac OS 8, running in an Electron app pretending to be a 1991 Macintosh Quadra. Yes, it's the full thing.
Via Dan Moren:
I fired it up to take it for a spin and it worked pretty well, though I did run into some bugs with scrolling (the scroll box doesn’t really move, though you can scroll down). It’s been pre-loaded with some games and demos, which Rieseberg apparently sourced from a Macworld Demo CD.
It’s even got Netscape, although the Internet connection doesn’t work.
Previously: