A literal digital Index Card Box? Perhaps Decker
I am surprised that no one has created a literal index card box, digitally. Rendering an actual box, actual drawers, and a search function to pick out a card.
I will say this, the closest I have seen is a small program on itchio called Decker
It is a recreation and expansion of the old index card mac program (back when Apple still looked like the fruit), very versatile, very user- supported.
I designed a primitive template to use as index cards. Linking cards is not fluid, but maybe someone will make a deck that does that.
Check it out.
Howdy, Stranger!