If you want to understand how he brings graphics to a text display, to push the boundaries of the “automated ASCII art” on a Commodore Pet, or Petscii Art:
The primary target audience is hobbyists (in particular people within the retro-computing community), non- or semi-professionals and education. The component directory contains many parts that were common on the 70s, 80s and 90s, like TTL logic and 8-bit CPUs and memories. The selection of the physical parts are bread-board friendly (e.g. DIP packages).
There is also a Youtube channel with some information about KretSim: https://www.youtube.com/channel/UClwSyaPo_9NFgxgMUCDrgdA