Too Long; Didn't Read
Decentralized applications don’t actually need to run on top of a blockchain network. Pinnacle, BitTorrent, Popcorn Time, and BitMessage, are models for decentralized applications that unexpectedly spike in sought after for a P2P association, anyway not on a blockchain. The front end of a decentralized application tends to be what you see and the back end addresses the entire business logic. Smart contracts are major design squares of blockchains, that communicate information from external sensors or events and help the blockchain manage the state of all network actors.