nLab

The nLab is a wiki for research-level notes, expositions and collaborative work. It includes original research in mathematics, physics, and philosophy with a focus on methods from type theory, category theory, and homotopy theory. The nLab espouses the "n-point of view" (a deliberate pun on Wikipedia's "neutral point of view"), which is that type theory, homotopy theory, category theory, and higher category theory provide a useful, unifying viewpoint for mathematics, physics and philosophy.

The n in n-point of view could refer to either n-categories as found in higher category theory, n-groupoids as found in both homotopy theory and higher category theory, or n-types as found in homotopy type theory.