As more and more people switch from physical books to electronic books, it has become increasingly important to have a reliable and user-friendly ebook reader. Fortunately, there are several excellent ebook readers available for Mac users, many of which are free. Here are the best free ebook or EPUB readers on the Mac App Store.

1. Apple Books: Apple Books (formerly known as iBooks) is the default ebook reader for Mac users. It is a simple and user-friendly app that allows you to read all your ebooks in one place. You can download books from the Apple Books store, import your own EPUB files, or even use the app to read PDFs.

2. Kindle: Amazon’s Kindle app is a great option for Mac users who prefer to read Kindle ebooks. You can download books directly from Amazon, and the app syncs with your Kindle account so you can access all your books across all your devices. The app also offers several customization options, making it easy to adjust font size, margins, and more.

3. Nook: Barnes & Noble’s Nook app is another great option for Mac users. Like the Kindle app, you can download books directly from Barnes & Noble, and the app syncs with your Nook account so you can access all your books across all your devices. The app has a simple and intuitive interface, and you can customize the font, size, and color of the text.

4. Calibre: Calibre is a free and open-source ebook manager that also functions as an ebook reader. It supports a wide range of ebook formats, including EPUB, MOBI, and PDF, and you can use it to organize your ebooks, convert them to different formats, and even download news articles and web pages. The app’s interface is a bit clunky, but it’s incredibly powerful and versatile.

5. FBReader: FBReader is a cross-platform ebook reader that supports EPUB, MOBI, and other ebook formats. It has a simple and customizable interface, and you can adjust the font, size, and color of the text to your liking. The app also offers several reading modes, including day and night modes, as well as support for bookmarks and annotations.

6. Kobo: Kobo is a popular ebook retailer and reader that offer a Mac app. Like the Kindle and Nook apps, you can download books directly from the Kobo store, and the app syncs with your Kobo account across devices. The app has a clean and user-friendly interface, and you can customize the font, size, and color of the text.

In conclusion, these are the best free ebook or EPUB readers available on the Mac App Store. They all offer a range of features and customization options, so it’s worth trying out a few to see which one works best for you. Whether you prefer to read on your Mac or on-the-go, there is an ebook reader out there that will meet your needs.