Always In Key is a small utility app that allows a user to select a musical key and restrict the MIDI output to only notes contained in that key. (For example, in the key of C Major, no sharps or flat will be played). When a "bad" note is received (i.e. a note outside the selected key), the user can configure AIK to either ignore the note or play an adjacent note.
RORY There should be a way to make your own scales. What I mean is selecting which notes are allowed and which aren't instead of choosing major or minor. And as David said, there is no use for this because most songs are not entirely in a scale. (Version 0.6)