As of 2020's, it is basically a cheap/slow/simple CPU used in embedded system applications.
It is interpreted. It actually implements a Python (-like ?) interpreter that can run on a microcontroller. See e.g.: Compile MicroPython code for Micro Bit locally.
As a result, it is both very convenient, as it does not require a C toolchain to build for, but also very slow and produces larger images.
The first thing you must understand is the Classic RISC pipeline with a concrete example.
The good:
  • slick UI! But very hard to read characters, they're way too small.
  • attempts to show state diffs with a flash. But it goes by too fast, would be better if it were more permanent
  • Reverse debugging
The bad:
  • educational ISA
  • unclear what flags mean from UI, no explanation on hover. Likely the authors assume knowledge of the Y86 book.
The good:
The bad:
  • Clunky UI
  • circuit diagram doesn't show any state??