The A9.com service, which is still in test mode, was released without fanfare yesterday.
It looks like all the others it offers a Web site and an Internet Explorer toolbar from which users can enter search terms. The searches can be limited to just Amazon.com products as well as the text of books available at Amazon.com.
Ironically A9.com's service relies on Google, which supplies many of the search results, and Amazon's own Alexa subsidiary, which provides traffic, other sites of interest and information on Web sites.
Amazon is keeping quiet about whether it plans to create its own search technology. µ