Google Sets was a Google Labs site that never became a first-class product. Its purpose was to accept a few phrases and return a set of related phrases. For example, sending “yellow”, “red” as inputs, Sets would return a list of “green”, “blue”, “orange”, etc.
As part of their recent re-focusing of effort they have shut down Sets along with other lab experiments. It wasn’t perfect and there were often irrelevant results mixed with the relevant, but it was the best tool for discovering alternatives if you only knew one or two items in a space. In commemoration, here is my last Sets search, for finding alternatives to ‘Mailchimp’.