Someone just pointed me to this question. I have one!
It’s called WhirlyGlobe and it’s built specifically for this purpose. Runs on ios, uses a combo of Objective-C and C++ and is very Cocoa Touch friendly. Uses delegates for camera motion, multithreaded, all that good stuff.
Oh, and it’s freely available under the Apache2 license.
Details can be found here:
http://mousebird.github.io/WhirlyGlobe/