offbeat vs quirky

offbeat is a noun but quirky is not a noun.

Word	Noun	Adjective	Verb	Adverb
offbeat	Yes	Yes	No	No
quirky	No	Yes	No	No

As adjectives, offbeat and quirky are synonyms defined as:

Other synonyms of offbeat include far-out, kinky, way-out.

offbeat (noun)	quirky (noun)
an unaccented beat (especially the last beat of a measure)

offbeat (adjective)	quirky (adjective)
(informal) strikingly unconventional	(informal) strikingly unconventional