Arguably another early pioneer of crossover was the twentieth century composer Kurt Weill. A writer of avant garde serious music, his collaborations with playwright Bertolt Brecht on projects such as The Threepenny Opera nevertheless gave an early indication of his interest in writing in an easily accessible, popular musical style. This trend in his work came to full fruition in later life in the United States, where he switched primarily to writing the scores for Broadway musicals such as Knickerbocker Holiday and One Touch of Venus. Some of the hits from those shows, such as September Song and Speak Low, are better remembered than the musicals from which they came.