SeeScore is built around a cross-platform MusicXML rendering engine which is available for use under license. Currently there are versions for iOS and Mac OS X.
This is an easy-to-use component using SeeScoreLib for dropping into your iOS (iPad or iPhone) app in Xcode's Interface Builder to give a SeeScore-like display of a MusicXML file.
You can download free demonstration versions of the SeeScore SDKs.
The iOS SDK is available here, including the SeeScoreLib framework, SSScrollView and a sample project which shows how to display MusicXML in your own iPad or iPhone app.
The OS X SDK is available here, including the SeeScoreLib framework and a sample project which shows how to display MusicXML in your own OS X app.
Please contact support for details about the fully licensed SDK.
If you are interested in displaying MusicXML on another platform please contact support.