I had never heard of this, and the repo doesn't provide a lot of background ... it seems to be a handheld (!) pen with interactive point-for-audio features, for 2+ year-olds.
Here [1] is the Ravensburger product page in German and here [2] is some toy seller's page.
The pen's main function is to point at things in the TipToi books and its integrated speaker explains the thing being pointed at, or plays a song or whatever the book is about. There is a huge catalogue of books for e.g. learning names of things in the kitchen, at a farm, fairy tales and even languages etc. It's great stuff and works well
There are different models and the newest one has a record feature as well as wifi (for asset downloads, versions before need a download companion app on the PC/mac).
TL; DR: the tip of a pen has a sensor, the books have dot patterns overlaid on top of image areas, the patterns are decipherable into (hexa-)decimal code, and with a script file the codes do different actions (set a variable, play an audio file).
Here [1] is the Ravensburger product page in German and here [2] is some toy seller's page.
[1]: https://www.ravensburger.de/de-DE/produkte/tiptoi
[2]: https://www.playpolis.com/ravensburger/tiptoi