Username or EmailPassword
Speaking as a former Newton developer, I'd disagree with your characterisation that Newton OS as not being application-centric and built around the notebook.
Newton OS was most definitely built around apps. Notepad was just the default app - later versions of the OS would let you swap that default to any other app. If you set Dates (for example) as the default app then Notepad would turn up in the Extras drawer and you could launch it from there.
The three main apps (Notepad, Dates, and Names) were all separate apps. The OS supported a 'windowed' view system, so Names would sit above other apps - and smaller 'utility' apps were not forced to run full-screen.
The OS was a highly dynamic object-oriented environment which would let third parties build extensions for the inbuilt apps. For example you could have extensions that would add new "stationary" types to the Notepad, or new card types to the Names app. All data was stored in "soups" - a dynamic OO database system. There was an OS-wide extensible "routing system" which was how you'd send emails, print, or fax - routing extensions were automatically made available in all apps.
In many ways it was a significantly more advanced OS than anything we have today. I often wonder what it would have developed into had it not been canned.