On-line proof checker, and texts.

Interactive tutorial for critical thinking.

Problems on translation into a logical system, drawn from the current news and updated daily.

Hyperproof, Tarski's World, Turing's World, and The Language of First-order Logic, educational logic software by Jon Barwise and John Etchemendy

Mathematical games from a logical point of view: strategies for games and using games in descriptive complexity.

Exploring the logical basis and practical meaning of infinite sets.

Contains an introduction to logic and formal systems, revolving around the Mizar proof checker, and a guide to Mizar.

A course in basic logic consisting of 5 studies with exercises and answers to promote the learning of logic. Homeschool, college, and seminary students.

(Hyper)textbook for students in mathematical logic, by Karlis Podnieks.

G.J.Chaitin's proof of Gödel's theorem using arguments having an algorithmic information theory flavor.