AIY Projects is a voice projects powered by google(at aiyprojects.withgoogle.com/voice#project-overview). I got the kit free with the MagPi magazine. I've got it to detect words and say something in response (I say"My name is James" and it says"Hello, I hear you have a blog").
I have considered a few projects e.g. a program were the computer sings (la, laaaa) and you have to sing the right pitch back (it is very hard to detect the pitch though).