Alexa opened its search index: http://websearch.alexa.com/welcome.html They too are owned by Amazon.

Also, look into this: http://www.opensearch.org/Home It's A9's search spec.

A9 is open, though afaik its not good (read big,exhaustive etc.) enough to provide an adequate platform to build something on. Amazon, it seems had their google strategy worked out EC2-S3-A9 though A9 is the weak link which yahoo search can fill.