TGD stands for Topological GeometroDynamics, a theory of everything due to the Finnish physicist Matti Pitkänen. It is a theory of branes in a specific higher-dimensional space, first published in 1983 (thus preceding even the supermembrane research of the 1980s, let alone the D-brane revolution in string theory of the 1990s). Fundamental particles are actually different topological structures in the branes. These structures can also occur at different discrete scales apart from the one that produces the standard model; these other scales give rise to dark matter.
Along with providing an explanation for fundamental physical phenomena, more controversially, Pitkänen also wants to use the physics of TGD's other scales to explain paranormal and anomalous phenomena that have been reported by various scientific dissidents. For example, spiritualists often talk about a "subtle body", and Pitkänen proposes that this arises from the "dark matter" excitations associated with the normal visible body.
He is also interested (as are the most avantgarde string theorists) in grounding TGD mathematically in concepts like Langlands number theory; and also in the ontological identifications that will allow consciousness to be explained. It is these two which provide the occasion for this post.
In his latest blog post, he asks whether the p-adic algebra of "Witt vectors" can describe both fundamental space-time structures, and play a role in "mathematical cognition". I haven't had time to look at the details at all, but it's very much the kind of proposal that interests me. (Shanna Dobson provides another example, e.g. see her coauthored paper on using "perfectoid diamonds" to model higher-order thought.)