These are what I use when I’m creating an ePub book. Your mileage may vary. For what it’s worth, I work on a MacBook Pro.

I use other tools as well for text manipulation, but this is the minimal set, apart from a text editor, for working with ePub books.

Info-ZIP

It can exclude extra file attributes, which is necessary because otherwise your ePub book can’t be read. I’m not sure if other versions can do the same.

Adobe Digital Editions

The best way to look at your work as it implements more of the ePub spec than any other software currently.

EpubCheck

The best way to check your work’s structure for errors; even a small mistake may result in, say, table of contents not working. Adobe Digital Editions will not display the specific error, even if it’s a fatal one, but epubcheck will.