ncatlab.org
Unknown
nLab (ncatlab.org) is a collaborative online wiki devoted to category theory and related areas of mathematics and philosophy. It hosts extensive, interconnected articles on categorical logic, topos theory, higher categories, and other foundational topics with definitions, explanations, and references.
More resources on Categorical Logic
Toposes, Triples and Theories
Free online book on topos theory and categorical logic
nLab: Categorical Logic
Comprehensive overview and references on categorical logic
mathworld.wolfram.com
MathWorld is Wolfram's comprehensive online math encyclopedia offering concise articles on mathematical concepts, including logic and category theory. The site provides definitions, explanations, formulas, and diagrams to help learners understand topics such as categorical logic.
ocw.mit.edu
MIT OpenCourseWare offers free, openly accessible MIT course materials—lecture notes, assignments, exams, and sometimes videos—across hundreds of subjects. You can browse by course to study topics like logic and categorical logic with downloadable resources for self-guided learning.