Google Sets Alternative

Onelook Thesaurus and Reverse Dictionary lets you describe a concept and get back a list of words and phrases related to that concept. Your description can be anything at all: a single word, a few words, or even a whole sentence. Type in your description and hit Enter (or select a word that shows up in the autocomplete preview) to see the related words.

A tool for finding similar collections of words, and not just those found in a Thesaurus.