AI that plays Quoridor?
I made an AI agent playing Quoridor. You can play against it right on the browser here: https://gorisanson.github.io/quoridor-ai/. As you can read on the "about" section on the page, I imitated the demonstration model of Daniel Borowski's Quoridor AI (https://danielborowski.github.io/site/quoridor-ai/display.html).

Martijn van Steenbergen's Quoridor program source code in Java (which maybe had been on the link https://code.google.com/p/quoridorai/ of Tom Wilkinson's answer) is now available on https://github.com/MedeaMelana/quoridorai. When I compiled the source code by Java 8 (JDK), it ran well.