now vs today

now and today both are nouns.

Word	Noun	Adjective	Verb	Adverb
now	Yes	No	No	Yes
today	Yes	No	No	Yes

As adverbs, now and today are synonyms defined as:

Other synonyms of now include nowadays.

now (noun)	today (noun)
the momentary present	the present time or age
	the day that includes the present moment (as opposed to yesterday or tomorrow)

now (adverb)	today (adverb)
in these times	on this day as distinct from yesterday or tomorrow
without delay or hesitation; with no time intervening	in these times
used to preface a command or reproof or request
at the present moment
in the historical present; at this point in the narration of a series of past events
in the immediate past
(prefatory or transitional) indicates a change of subject or activity