In his papers on qualitative logic, entitative graphs, and existential graphs, Peirce developed several versions of a graphical formalism, or a graph-theoretic formal language, designed to be interpreted for logic.
In the century since Peirce initiated this line of development, a variety of formal systems have branched out from what is abstractly the same formal base of graph-theoretic structures.
- Logical Graph @ Commens Dictionary of Peirce's Terms
- Existential Graphs, Jay Zeman, ed., U. of Florida. With 4 works by Peirce.
- Frithjof Dau's page of readings and links on existential graphs includes lists of: books exclusively on existential graphs; books containing existential graphs; articles; and some links and downloadables.
- The literature of C.S. Peirce’s Existential Graphs (via Internet Archive), Xin-Wen Liu, Institute of Philosophy, Chinese Academy of Social Sciences, Beijing, PRC. A whole lot there.