A free program for Android, by Roni Music.

Amazing Slow Downer Lite is a free and easy-to-use app for Android devices that allows you to edit an audio file to repeat sections of the music or to slow down the speed without changing the pitch or tone.

It has a built-in music player for to check the music you edited.

To change the speed, simply touch the slider on the right side of the window and drag it to the desired speed. You can adjust the speed between 25% to 200% of the original speed of the file.