A new Operating System is incredibly hard to distribute.

The OS normally runs at the level of the hardware, and getting people to buy new hardware is a challenge.

That, and every new OS needs a whole new ecosystem of software; it's very hard to get to a critical mass of software.

But what if you made an OS distributed in the browser?

As far as the browser is concerned, it's just any other webpage.

A pocket universe with alternate laws of physics that manifests in a browser tab.