Strum Machine Strum Machine is an indispensable app for creating play along jam tracks from your mobile device. You can modify existing or create new chord charts, pick the rhythm instruments to accompany you, and set the song key and tempo. This is a great app for learning new songs, woodshedding difficult sections or working on improvisation. Just a few of the features include auto-speedup feature, you can save to multiple song lists, the app works offline, you can print charts, the app has an integrated notepad and you can share your song lists with your friends. I use this app every day.