Historically, Smalltalk has many browsers (views). This System Browser is one of many browsers, and the most busy-looking.
You can browse within it, and also spawn off other kinds of browsers from it.
And these browsers are extensible with others. As someone new to Smalltalk, I was pretty easily able to add a visual class hierarchy browser into this environment:
https://www.neilvandyke.org/smalltalk-chg/
Half the things we know or think about in HCI, the people at PARC figured out before we were born, and sometimes before the hardware to test it existed.
Including how to build a full workstation with memory safe systems languages, besides Smalltalk,
Interlisp-D, now recovered and playable in the browser,
https://interlisp.org/
Mesa with XDE (think the safety Zig is selling today, but in 1985)
http://bitsavers.informatik.uni-stuttgart.de/pdf//xerox/xde/...
Cedar, a full graphics workstation in the evolution of Mesa, now with proper mix of reference counting + cycle collector, as full GC implementation,
Here the demo done by Eric Bier for the Computer History Museum,
https://www.youtube.com/watch?v=z_dt7NG38V4