Hooray! We don't need composers anymore! We have Microsoft Songsmith.

Read more here about Microsoft Songsmith.

Songsmith generates musical accompaniment to match a singer's voice. Just
choose a musical style, sing into your PC's microphone, and Songsmith will
create backing music for you. Then share your songs with your friends and
family, post your songs online, or create your own music videos.

You can get the free trial here.