Tesseract - Tesseract is an optical character recognition engine for various operating systems
Capture2text - Capture2Text enables users to quickly OCR a portion of the screen using a keyboard shortcut.
GOCR - GOCR homepage. GOCR is an OCR (Optical Character Recognition) program, developed under the GNU Public License.
TextSniper - Instantly extract any text from your Mac's screen
TextGrabber - Office & Productivity
dpScreenOCR - Program to recognize text on screen