Zyzzyva is a very easy to use and efficient word study OS X application. Zyzzyva's OWL2+LWL lexicon is 100% accurate as verified by the metrics available on the NSA Dictionary Committee's website.
Zyzzyva has been used successfully as a Word Judge at many North American SCRABBLE tournaments, including BAT, Oregon TILE, the Dallas Open, the U.S. SCRABBLE Open and the National School SCRABBLE Championship!