Tesseract - Tesseract is an optical character recognition engine for various operating systems
NAPS2 - NAPS2 is a document scanning application with a focus on simplicity and ease of use.
Onlineocr.net - Free Online OCR service allows you to convert PDF document to MS Word file, scanned images to editable text formats and extract text from JPEG/TIFF/BMP files
Simple Scan - Project information. Part of: The Gnome Project. Maintainer: Simple Scan Development Team. Driver: Simple Scan Development Team. Licence: GNU GPL v3.
Prizmo - Prizmo is a scanning application for Mac with Optical Character Recognition (OCR) in over 40 languages with powerful editing capability, text-to-speech, and iCloud support.
XSane - A good proposal for SANE-2 has been written.