I am excited about the brand new version of Circle Theory that recently went live on the App Store. A handful of bugs were fixed, and the entire inner core of the App was rewritten to be more efficient and testable. (Now no more old bugs should ever creep back in accidentally.)
The biggest new addition, and often requested feature by many, is the ability to play notes. Circle Theory now has the ability to show notes on a staff and play scales in the dialed-in key signature. Give it a try!