I make the version used for the demonstration at ICFP'01 available here for people interested in exploring the proposed type and type error explanation method. I will continue developing it (however, this is not my main task).
Load it into Hugs98 and evaluate main. The current textual user interface is rather simple and the implementation of the user interface is terrible. You first have to choose an example program and then choose between free navigation and algorithmic debugging. Both have many variants, the command ? gives an overview of the available commands. All examples are hard-coded in abstract syntax at the end of the source code. It should not be too difficult to add further examples. If you have interesting examples, please send them to me, just like any comments you have.TypeIlluminator currently handles class contexts, but it does not yet help understanding them.
Note that the source contains code of Mark Jones' Typing Haskell in Haskell.