Along with Apple Books to view the EPUB on any Apple device or macOS 10.9 and later, we recommend some optional but useful free software to help view and test your files:
Thorium from EDRLab view an EPUB on Mac or Windows PCs.
Pagina EPUB-Checker for EPUB validation. If present on your Mac then CircularFLO will use this tool to validate your EPUBs as they are created.
Ace, by DAISY to run extra accessibility checks on your valid EPUB. If present on your Mac then CircularFLO will use this tool to run accessibility checks to your EPUBs as they are created.
Kindle Previewer to convert, preview and export your Amazon files.
MasterPlan from Circular Software to securely publish your ebooks online. Free to use for CircularFLO Pro customers.