can you download nook on mac

Not the device, but there is a compatible app. Look here: Free NOOK Reading App - Barnes&Noble.

Barnes & Noble no longer supports the "Nook" app on OS X (or Windows.) There is a download, but it's described as "not compatible with 10.8." Presumably it's not compatible with later versions of OS X either.

http://www.barnesandnoble.com/u/nook-for-mac/379003592/