Serial music, which is mainly non-tonal, superimposes compositional freedom onto an unusually rigorous process of pitch-sequence transformations based on ‘tone rows’: a row is usually a sequence of notes using each of the 12 chromatic pitches once. Compositional freedom comprises forming chords from the sequences, and in multi-strand music, also in simultaneously presenting different segments of pitch-sequences. The present project coded a real-time serial music composer for automatic or interactive music performance. This Serial Keyboardist Collaborator can perform keyboard music which is impossible for a human to realize. Surprisingly, it was also useful in making more tonal music based on the same rigorous pitch-sequence generation.