Written by Tim Thompson, KeyKit is a versitile and extensible program, as KeyKit is both a composition program and a programming language. Many different 'tools' for creating music. David Wools has written a number of interesting such 'plugins', several named Wools BarGen and another called Very Structured Melody Maker (VSMM).
Experiment using an ArtSong MIDI process through KeyKit Markov Maker
Created with KeyKit, using David Wools Very Structured Melody Maker Tool