This list can of course never be complete, but should give an overview of what is currently available on the web.
Propositional Calculator to test simple propositional formulas. Written in Java; they used a parser generator called Jack to build their parser (Maybe that could become handy for extending our tool to calculate extensions for arbitrary theories).
There are some Default Logic examples given, including JAVA-demos, among these the famous ``Tweety'' example. The user can choose truth-values of the initial knowledge and watch the effects on the extensions.
This work is not new (around 1995) but Mr Jeansoulin still works with default logic using it in GIS (Graphical Information Systems). In that context, it is interesting to mention that he works on a project together with Prof. Andrew Frank at the TU Vienna.
Another simple calculator for propositional logic. No special features.
The Logics Workbench is a software environment that allows to deal with different kinds of propositional logics including nonmonotonic approaches, developed at the University of Bern. It provides also modules for default logic, circumscription, autoepistemic logic and modal logics.
The software is available for different platforms including Solaris and Linux and they also have a cgi-based interface to the web.
This Site provides some tools including a proof builder and a proof checker for propositional logic. Syntax and notation are taken from E.J. Lemmon's book Beginning Logic or Colin Allen's book Logic Primer.
The author:``My Gateway to Logic ... displays several kinds of logical diagrams and performs various other logical functions is rated ``top 25%'' by JARS and considered cool by Gamelan.''
Two applets about Quantum logic, a non-distributive subset of classical logic:
``The two quantum logic applets on this site are interactive proof-checkers for propositional quantum logic, and predicate quantum logic. The two logics are based on E.J. Lemmon's systems for classical logic, described in his book Beginning Logic.''
This site contains a proof checker where you can enter a sequent you attempt to prove, and your proof will be checked. Test your knowledge of logic in the ``Logic Quizmaster'' section!
This tool was created by Collin Allen (Author of the book Logic Primer already mentioned aoove), whose homepage is also worth visiting.
An online logic tutorial with many interactive exercices and examples.
Interpreting language in formal logic, by examples. Two very basic examples to understand logic, but worth looking, if you don't have an idea how to read und understand logic sentences at all.
This page generates random truth table problems with two variables, which should be completed by the user.
Another nice tool to learn logic basics.
``Provability of formulas in several logics, validity of formulas in a model, drawing and editing Kripke models and models for dynamic logic.''
Nice layout, cool features, but seems still under construction after a first glance... didn't really work.
Funny links can be found here, but anyway there are also quite useful logics and mathematics sections .
For all applets the Java-1.2.1-Plugin is needed.
Some of the tools which are accessible online via web can be found above.