Anything that uses 9 of the 12 tones in a Western standard equally tempered octave, for starters. So, if it changes key at any point it is very likely to find t

Anything that uses 9 of the 12 tones in a Western standard equally tempered octave, for starters. So, if it changes key at any point it is very likely to find that it uses 9 tones or more. Anything written in a melodic minor scale will use 10 tones, as the 6th and 7th of the melodic minor scale are sharpened on ascending movement but not sharpened on descending. Assuming it uses every note in the scale of course - not all melodies do. But if you start off saying 8 tones per octave you're probably not making space for sharpened 6ths by ignoring the 4ths. Just about anything written by Schoenberg in accordance with his theory of tone rows and atonality, where the idea is to use all 12 tones as a fundamental component of your melody so that you're not constrained by the notion he didn't like of a tonal centre. Okay so this isn't a popular genre, because it turns out most people who aren't Schoenberg really rather like tonal music. (Yes, that's an oversimplification of his ideas, he did a lot more for music than that). I think the author of the article has exaggerated the claims about "every possible melody", because given the people who did it are musicians themselves they must be well aware that they've ignored a large swathe of music, and that's before we've even considered tuning systems which don't have 12 tones per octave.