Tip of my Tongue helps you find the words that you fall just too short of remembering. It could also function as a reverse dictionary tool: simply enter a phrase or concept, and this app will give you individual words related to the concept.

The application also groups words by their part of speech.
syn: Synoynm
n: noun
v: proposition
adj: adjective
adv: adverb
ant: antonym

This app would not be made possible without the folks from DataMuse. Their API can be found here: http://www.datamuse.com/api/