Music theory from the command line.
$ cmaj --scale=Em
E F# G A B C D
$ cmaj --scale=Bbm
Bb C Db Eb F Gb Ab
$ cmaj --scale=C
C D E F G A B
$ cmaj --chord=C
C E G
$ cmaj --chord=Em9
E G B D F#
$ cmaj --chord=DM9
D F# A C# E
$ cmaj --freq 440 3
1320
Want to know more? Check out the docs for an exhaustive list of every option.