openmind.org
Open Mind is a project to create a vast collection of common sense knowledge by involving people all over the world, each contributing a small amount. It's sort of meant to be an open-source version of CYC.
To participate, you create an Open Mind account (simple and fast), and then you start doing "activities". each activity is structured so that Open Mind gives you a topic or a statement and you elaborate on it with additional information. For example, in the What else should I know? activity, you are given a statement like "Bob bought some milk" and provide additional statements such as "Bob probably used money to buy the milk" and "Milk is a kind of food".
The idea is that with thousands of contributors (13,823 registered users currently) contributing facts (678,329 database entries currently), Open Mind will eventually develop the common sense knowledge of, say, a five-year-old child.
Having looked through some Open Mind papers, I'm still unclear on what they actually do with the information people provide (most of it as free English text) in order to build a database. They may just keep the English around, planning to process it on demand later. They may do some kind of parsing or lightweight linguistic extraction. Perhaps they look for the co-occurrence of words to build a sort of semantic network.
Of course, it's also unclear whether this approach could work or, if it could work, how much data you have to have before the whole thing become useful. Does Open Mind have a Skynet moment?