gtkguitune software package provides Guitar and other instruments tuner, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install gtkguitune
gtkguitune is installed in your system.
Make ensure the gtkguitune package were installed using the commands given below,
$ sudo dpkg-query -l | grep gtkguitune *
You will get with gtkguitune package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | X Window System software |
| Package | gtkguitune |
| Version | 0.8-6+b2 [amd64, arm64, armel, |
| Description | Guitar and other instruments tuner |
| Sub Section | x11 |