Iris is an interactive voice automated desktop assistant (GPLv2).  From their website (they are also on GitHub):

Iris will listen to what you say, use Google's Voice Recognition servers to generate text from speech, then parse your text and find a short answer from freely available sources like Wikipedia.

[...] Iris was design for users to ask questions natural, in grammatically correct English. Iris utilizes natural language processing to understand what exactly what is being asked. 

--- (Edited on 9/8/2011 2:47 pm [GMT-0400] by kmaclean) ---