Synthesized MIDI rendering of Guillaume Dufay's "Ave Regina", c.1450, Ox. Bod. Can. misc. 213 f.62, after facsimile in W. Apel, The Notation of Polyphonic Music (1960), facs. 26. Created with Lilypond.
Example of atonal music which avoids octaves, avoids major and minor triads, avoids more than three notes from the same diatonic scale, and avoids conjunct melodies/uses disjunct melodies. From Schoenberg's Klavierstucke, Op. 11, No. 1.