GUV Tuner is an accurate and customizable tuning app created by musicians (under the most generous definition of musician).
By default, the app is suitable for tuning guitar, ukulele and violin, or you can make your own alternate tuning with whichever notes you want (Led Zeppelin fans need this).
Your tunings are saved securely to your iCloud and synced across devices.
GUV Tuner is suitable for tuning many instruments, e.g. electric guitar, acoustic guitar, bass, ukulele, mandolin, banjo, violin, viola and cello.