Cyc, the largest expert system ever to be built, is to have a small subset released to the public in the form of OpenCyc -- an embeddable, developmental version of the knowledge base. Cyc works by associations and assertation; philosophers input fundamental truths and the system requests clarifications about ambiguities. It's all pretty vague, and the article in the LA Times, Birth of a Thinking Machine, doesn't clear much up, but what it does say is extremely interesting.
The Slashdot thread contains some interesting comments about the computer race from the 1980s that never happened: "CYC is one of the few survivors of the "A.I." speculative bubble of the mid-1980s. Though this bubble was not as large as the recent InterNet bubble, there was a lot of hype. The US computer industry feared it would lose the "A.I. war" against Japan's "Fifth Generation Project". This project was going to build an intelligent supercomputer using expert systems. It was almost a complete bust." Hey, I remember that! Weren't the Japanese going to hook together a million artificial neurons in a ten year project and then just, um, switch it on and see what happened?