Google Sets was created in the early stages of the Google Labs incubator. It allowed users to enter a few example words, and the software would generate a list of suggestions (sets) based on the examples:
For example, if you’d enter Ford and Toyota, Google Sets would generate a long list of car brands.
The patent was filed by Simon Tang and Jeff Dean – computer engineers who contributed to the creation of Google’s ranking algorithm, the targeting algorithm of AdSense, the spam detection learning algorithm of Gmail, Google’s crawling, indexing, and serving systems, and more.
The tool was likely discontinued because it didn’t see a lot of use. The prototype never graduated from the incubator into a full product.
That said, while Google Sets is unavailable to users, it’s fairly likely that Google has integrated its functionality in its search algorithm in order to help it understand search intent and related searches better.