Zcash is a cryptocurrency as well as Bitcoin. But it's not the
same thing.
When Bitcoin was first released, it brought an open financial
system to the world. Anyone could connect without requiring
permission from anyone else; anyone could extend and improve on it
without permission.
However, it came with a drawback - privacy. Bitcoin allowed
everyone to see the sending address, recipient address, and value
of all transactions on the blockchain. Sure, they weren't tied to a
user (or computer) by default, but contamination was a possibility.
People are, after all, only human. In contrast, Zcash automatically
hides the sending address, recipient address and the value of all
transactions - unless you have the viewing key.
The Zcash team was founded with privacy in mind: privacy for
businesses; privacy for commerce. To be viable long-term,
tangibility is needed - and without privacy, tangibility can't
exist. Bitcoin brought tangibility to the digital world, but Zcash
is making it accessible. No longer do coins need to be tumbled; no
longer do new addresses need to be generated for each transaction
to ensure complete anonymity. It's built in from the get-go.