Quarter Tones
Since Music Publisher 6 the software has been able to create and hear scores using Quarter Tones.
Quarter tones are, as the name suggests, notes placed exactly half way between those normally part of Western Music.
So between C and C sharp there is C half-sharp; between E and F there is E half-sharp.
Just as C sharp can be D flat, C half-sharp can be D three-quarter flat; E half-sharp can be F half-flat.
In fact we need new symbols and while there is not yet 100% agreement on the symbols, a set of symbols is gaining universal acceptance.
Here is a scale involving all the 24 quartertones:

Click the image to hear the scale. (The actual quality of the sound you hear depends on your sound card.)
And this score demonstrates the difference between major, minor and half-minor triads:

Again, click the image to hear the effect. And if you don't wince I think you should have.
All pictures and sounds produced by Music Publisher.