From this answer, there are quite a few.
Tesjeract (http://code.google.com/p/tesjeract/), a JNI Wrapper for Tesseract (http://tesseract-ocr.googlecode.com/).
Very nice write up on this: http://www.itwizard.ro/interfacing-cc-libraries-via-jni-example-tesseract-163.html
Example of it in practice: Mezzofanti (http://code.google.com/p/mezzofanti/), an open-source Android App using Tesjeract
