There is a terminal package called Tesseract you could use, and is of course, free. If there’s a specific OCR task (e.g., OCRing PDFs, or converting a jpeg to an OCR’d PDF) you can just write an alias for the command and the relevant arguments/options/flags.
DEVONthink Pro Office (and only the Pro Office, not Pro, and not Personal) come with ABBYY OCR. While the ABBYY OCR has fairly high accuracy, I do find it inflates file sizes A LOT unless you dramatically decrease the image quality. This works just fine for me if I’m doing receipts and invoices, but if I have long-form documents that need OCR I find this to be a problem because quality is much more important in those instances.