MyScript, the company I work for licenses closed-source handwriting recognition technology for desktops (windows, linux, osx), tablets(ios, android) as well as automotive (Audi navigation system).
Our developer portal is regularly updated with new content.
You can try our technology on our web demonstration portal (beware some version of the Evernote clipper severely break HTML canvas interaction).
We also have various applications available on iTunes for iOS devices and Google Play for Android devices.
Hope that helps.