> connecting to the chess engine that comes preinstalled on macOS

Can you elaborate on this please? The presentation at your link doesn't say.

One of the preinstalled apps on macOS is /Applications/Chess.app. Turns out it uses an open-source chess engine called sjeng, the binary for which is inside the app bundle. Chess.app is itself open source, so I tweaked Apple's code for my own purposes. The code launches an sjeng process, opens a pipe to it, and sends commands over the pipe.

There's a couple of sentences about this in the _README file here (as well as my tweaked source files):

https://github.com/aglee/ChessFidget/tree/master/ChessFidget...

Fun fact: you can play chess in a terminal window by running /Applications/Chess.app/Contents/Resources/sjeng.ChessEngine. You can enter the `help` command for instructions. Note this will create four files with .lrn extensions in your home directory. I forget how to control this behavior -- you can Google "sjeng" for details.

Thanks for the explanation!