Datamusic's FRACTAL MUSIC ST
FRACTAL MUSIC is a MIDI program for the Atari ST range of computers--a powerful Real-time music generator and processor written by Chris Sansom, a composer experienced in music ranging from pop songs to advanced contemporary orchestral music, with critical and technical advice from Laurence Glazier, an experienced computer programmer and the founder of Datamusic.
As a music generator, FRACTAL MUSIC: 

Produces billions of different musical combinations from Fractal Mathematics according to parameters set by the user; 
Incorporates Randomisable parameters; 
Has 16 tracks. 
The program uses a cyclical, iterative process from Fractals to generate monophonic lines of music. The process is 3-dimensional, affecting the pitch, placement in time and key velocity of each new note. The result is REAL MUSIC with melodic, rhythmic and dynamic interest--including rests! Recognisable near-repetitions of musical shapes occur frequently, lending extra validity to the musical output. It is possible for the user, by judicious setting of parameters (and with the editing features described below), to produce subtle variations on the same music in a number of different ways.
As a music processor, FRACTAL MUSIC offers extraordinary Music Editing facilities (and some standard ones), including:


Quantizing; 
Stretching and Squashing of pitch range; 
Lengthening and Shortening of time-scale, resulting in simultaneous different tempi; 
Transposition; 
Shifting backwards and forwards in time; 
Reflecting the music in an axis at any angle, with a selected note and time as origin ...

... with these short cuts:
   Inversion about any note (or between notes)--i.e. reflection in a
horizontal axi,
    Turning the music Backwards--i.e. reflection in a vertical axis;

Rotating the music through any angle, with a similarly selected origin ...

... with this short cut:
   Retrograde Inversion--equivalent to rotating through 180 degrees.

Some of these techniques (transposition, stretching, squashing, inversion, retrograde) have been familiar to composers for centuries. FRACTAL MUSIC does them automatically. Others (reflection, rotation) are logical extensions of these concepts, but extremely difficult and tedious to do manually.
Chris Sansom has already used these techniques in his serious compositions. 

Other features include:


Full two-way MIDI File compatibility, allowing the user to transfer the program's output to a sequencer for building up large-scale compositions, or to import other material into FRACTAL MUSIC in order to apply the program's special editing features, or any other combination the user wishes to dream up; 
FRACTAL MUSIC's own two file formats, for saving parameters only or parameters plus any MIDI data generated; 
Ability to run on all ST and STE machines (1 megabyte recommended, but not essential); 
Compatibility with monochrome or colour (medium resolution) systems; 
Tempo range of 41.18 to 480 beats per minute; 
Time resolution of 96 "ticks" per beat; 
Full implementation of the Atari ST's GEM interface, including menus, overlaid edit screens etc.; 
Checking of available memory or disk space, where appropriate, before each operation is carried out; 
Keyboard shortcuts for all mouse commands, plus some extra keyboard commands; 
Help screens giving keyboard commands at all points in the program; 
Full MIDI event list, on screen or printed out; 
Detailed print-outs of parameters (including random ones) set by the user; 
MIDI Thru, routed to any MIDI channel, allowing the user to select suitable sounds or play the keyboard while the program is loaded.