Zcash started as an alternative to Bitcoin; the Zerocoin protocol which was improved upon and launched as ZEC cryptocurrency in 2016. Like Bitcoin Zcash didn’t have an ICO on startup and is gotten purely through mining.
However, unlike Bitcoin which utilizes only blockchain technology for transaction, Zcash uses zk-snarks an extra optional encrypted and more secure system to ensure that all the information regarding user transactions is safely encrypted.