You're referring to iMitone, a music keyboard app that allows users to play music using their computer keyboard!
Here's a useful feature for the free version of iMitone Key: imitone key free
With Quick Start Mode, users can immediately start playing music with iMitone Key without having to navigate through multiple menus or settings. This feature will provide a streamlined experience for new users, allowing them to focus on making music. You're referring to iMitone, a music keyboard app
"Quick Start" Mode