For details, see wikipedia article.

In short, as a list:

Matt Mahoney in his Proposed Design for Distributed Artificial General Intelligence communicates an extremely interesting idea of the worldwide common knowledge space:

For the artificial intelligence, there is an important concept of the software capable of rewriting (or amending) its own source code. As a modification of this basic idea, an intelligent program might be able to write other (possibly intelligent) programs.

This is already happening. Some people call this the automation pressure, others refer to the informational society (as a kind of a post-industrial society). And this is where I see the purpose of creating an artificial intelligence.

Let me elaborate a bit.