You could have downloaded ePubChecker 1.1.1 for Mac from our software library for free. This free Mac application is an intellectual property of Rainwater Soft. The application relates to Productivity Tools.
From the developer:
ePubChecker™ is a free app to check your EPUB files for correct format.
To publish your Apple iBook, they require your manuscript be verified by the 'epubcheck' checking engine. Our tool 'ePubChecker' harnesses version 1.0.5 of that engine, making it easy to use on your Mac, PC, or Linux computer.
You may want to check out more software for Mac, such as ePub Checker, which might be similar to ePubChecker.