Reflow

Reflow is a music notation app that runs on iPhone, iPad and Mac. It is a 100% Native app that supports iCloud sync and latest Mac OS X features such as Versions, Autosave and Fullscreen.

You can create your own tablatures and sheet music, or read existing Guitar Pro and PowerTab files. It can be used to compose and practice any song for Guitar, Bass, Drums, Piano, Banjo, and many other instruments as long as it uses Standard Notation or Tablature.

The Reflow engine allows you to modify your song while it's still playing, for a totally non interruptive workflow, which is really nice!