ぜんぜん (zenzen) is an adverb that means 'not at all' or 'completely'. It is used to express the idea of negation or emphasizing that something does not happen or is not true.
全く (mattaku) - (N4) - Both ぜんぜん (zenzen) and 全く (mattaku) mean 'not at all' or 'completely'. However, 全く (mattaku) is more formal and can also mean 'entirely' or 'thoroughly'.
まったくも (mattaku mo) - (N4) - Both ぜんぜん (zenzen) and まったくも (mattaku mo) mean 'not at all' or 'completely'. However, まったくも (mattaku mo) is more emphatic and stronger in negation.
全然 (zenzen) - (N5) - ぜんぜん (zenzen) and 全然 (zenzen) have the same meaning and usage. The only difference is their formality level, with 全然 (zenzen) being more informal.