ai3gtmc (known as sanctifi3d on the QJ.Net Forums) has released a nifty application for PSP-carrying musicians to use. It's called the AIO Tuner, and it's essentially an app that helps help users tune their violin, guitar, or bass guitar.

As you can see in the above pictures, the AIO Tuner allows users to tune their guitars by playing the note that supposed to come out on a properly tuned instrument.

ai3gtmc notes that it's been tested on 3.90m33-2 for the Original PSP, and that it should work on other firmwares except 1.5. That being said, please remember to check the readme included in the download for additional information on this application.