Check out Visuwords. Cool word meaning/relationship visualization tool. Haven’t yet thought about how I’d actually use it in practical terms (other than as a fancy thesaurus), but darn it’s cool!
Actually, I learned a new word today, cassation, and it’s not in there. But a word I’ve always liked but only actually seen in a word-a-day calendar I had at least a decade ago, pertinacity, was in there and tied to all the words you’d expect it to be, and then some.