Flock

From the artist's page:

Flock is a full evening performance work for saxophone quartet, conceived to directly engage audiences in the composition of music by physically bringing them out of their seats and enfolding them into the creative process. During the performance, the four musicians and up to one hundred audience members move freely around the performance space. A computer vision system determines the locations of the audience members and musicians, and it uses that data to generate performance instructions for the saxophonists, who view them on wireless handheld displays mounted on their instruments. The data is also artistically rendered and projected on multiple video screens to provide a visual experience of the score.

Perhaps you've already seen it, but I really like aleatoric music.