Reverse Dictionary - Describe a concept and get back a list of words
Lexica - An open source word-search game.
Silicon Valley Dictionary - Urban dictionary meets Silicon Valley
Ruzzle - Ruzzle is a fun and fast-paced word game where you can challenge your friends or allow an opponent...
Dictionary Anywhere - Dictionary Anywhere is an open-source and easy-to-use browser extension for Mozilla Firefox and Google Chrome that allows you to check definitions easily while browsing the web.
Wordbase - Wordbase - the fun, addictive and challenging game of words and letters for iPhone!