Is there an open source implementation of Google AdWords, or is the technology protected in some way (such as being patented)?

Edit: To clarify, I'm looking for a 3rd party implementation of an AdWords-like system (that has nothing to to with Google AdWords beyond the concept and superficial similarity).

+3  A: 

Depending on what part of the system you are looking to replicate you should give OpenX ad server a try. You can install it on your own servers or use their hosted version. There are other open source ad servers but this one seems to work pretty well.

thanhks carson, I'll take a look
Ben Aston