Check out http://opencyc.org/
Opencyc 1.0 is a commonsense inference engine. It has:
# The entire Cyc ontology containing hundreds of thousands of terms, along with millions of assertions relating the terms to each other, forming an upper ontology whose domain is all of human consensus reality.
# English strings corresponding to all concept terms, to assist with search and display.
# A compiled version of the Cyc Inference Engine and the Cyc Knowledge Base Browser.
# Documentation and self-paced learning materials to help users achieve a basic- to intermediate-level understanding of the issues of knowledge representation and application development using Cyc.
# A specification of CycL, the language in which Cyc (and hence OpenCyc) is written.
# A specification of the Cyc API for application development.
I think this program is probably the most extensible and advanced basic AI framework openly available. The potential is awesome... I'm going to do more research into this area and see what I can come up with. Anyway, I thought that I'd share this here.
There are a few natural language interfaces for the Cyc system, I'll llist them later after I refind them