Karlheinz Stockhausen
From 1953 he worked seriously at electronic music.  He thought that electronic music was going to be the music of the future.  His Gesang der Jünglinge is a multi-track work, using 5 tracks (later reduced to 4).  Gruppen (Groups) is a work for three orchestras and three conductors.  They sit in different parts of the concert hall and play at different speeds at the same time.  His piano piece Klavierstück XI (Piano Piece eleven) shows no influence of John Cage at all.  The music is written on a huge sheet of paper and the pianist decides as he plays which part of the music to go to next and how to play it.  This means that each performance of the work is different.  This is not “chance” music, but "mobile" music.