Clara OCR is a free (GPL) OCR for systems that support the C library and the X windows system.
Cuneiform for Linux
Cuneiform was originally developed and open sourced by Cognitive technologies, and was originally Windows-only. This project aims to port Cuneiform to run natively on Linux.
GOCR is an OCR (Optical Character Recognition) program, developed under the GNU Public License.
Lector can help you scan your papers and create text documents. Lector lets you select areas on which you want to do OCR (Optical Character Recognition). Then you can run tesseract-ocr simply clicking a button.
moz-hocr-edit is a Firefox extension for editing hOCR documents.
OCRFeeder is a document layout analysis and optical character recognition system. Given the images it will automatically outline its contents, distinguish between what's graphics and text and perform OCR over the latter. It generates multiple formats being its main one ODT.
ocrodjvu is a wrapper for OCRopus, an OCR system, that allows you to perform OCR on DjVu files.
SILVERCODERS OCR Server
(commercial) SILVERCODERS OCR Server is a powerful and complete server-based optical character recognition (OCR) and PDF conversion solution for enterprises.