Wikipedia
OCRopus
OCRopus is a free document analysis and optical character recognition (OCR) system released under the Apache License, Version 2.0 with a very modular design through the use of plugins. These plugins allow OCRopus to swap out components easily.
OCRopus is currently developed under the lead of Thomas Breuel from the German Research Centre for Artificial Intelligence in Kaiserslautern, Germany and is sponsored by Google.
OCRopus is developed for Linux; however, users have reported success with OCRopus on Mac OS X and an application called TakOCR has been developed that installs OCRopus on Mac OS X and provides a simple droplet interface.