Aby Warburg used three primary tools for his research: his library, a card index, and panels.

His panels would be versions of pinboards, chalk boards, dry erase boards, or online versions of things like Canvas in Obsidian. It amounts to the ability to take notes or images on cards and shuffle them around on a table (or affixed to a wall).

Steiner, Benjamin. “Aby Warburgs Zettelkasten Nr. 2 ‘Geschichtsauffassung.’” In Zettelkästen. Maschinen der Phantasie, edited by Heike Gfrereis and Ellen Strittmatter, 154–61. Marbacher Kataloge 66. Marbach am Neckar, 2013. https://www.academia.edu/8637204/Aby_Warburgs_Zettelkasten_Nr_2_Geschichtsauffassung_.

machine translation:

Anyone who follows Warburg's list of notes is following his train of thought; from the banking system in Florence, medieval commercial society, the development of individuality, the restless professional work of the Calvinists and the reformed form of asceticism to Warburg's own origins in an old Jewish banking family. 378 The Zettelkasten is Warburg's Ariadne thread through his labyrinthine library and his labyrinthine thinking: from werewolf to history. A thought, an idea or a new concept does not emerge in a linear progression, but in a process of moving idea units and cross-references back and forth, which lasts until new interfaces and nodes have formed.