kobo, google, and some smaller ebook sites (which might just serve as an interface to kobo's catalog like walmart did). They almost always use adobe digital editions drm, but that's removable by the buyer with effort.
For free epub ebooks, there's overdrive and the library ecosystem; legal libraries also DRM-wrap their epubs.
This is the one case where I'm OK with DRM -- you're receiving the library's book on loan (it's never your book), and they need a way to enforce the length of the loan.
For free epub ebooks, there's overdrive and the library ecosystem; legal libraries also DRM-wrap their epubs.