Polkadot was developed by Gavin Wood, one of the original Ethereum founders and the developer of the Solidity (smart contract) coding language.
Parachains can be customized for any number of use cases and feed into the relay chain.
Polkadot shares many similarities in design and operation of Ethereum (once the upgrade to Ethereum 2.0 is completed). Both protocols operate a main blockchain where transactions are finalized and will allow for the creation of many smaller blockchains that leverage its resources. In addition, both protocols will use staking instead of mining as a means of keeping the network synchronized and secure.
The Polkadot protocol seamlessly connects public and private blockchains sharing a common security layer -allowing for tokens and transactions to be shared trustlessly between these independent blockchains.