There are three types of decentralized applications:
Type I decentralized applications that have their own block chain, such as Bitcoin.
Type II decentralized applications that use the blockchain of a type I but are protocols and have tokens that are necessary for their function like the Bitcoin Omni Layer.
Type III decentralized applications that use the protocol of a type II and are additionally protocols that have tokens necessary for their function, such as the SAFE Network that uses the Omni Protocol to issue safecoins.
Decentralized applications may run on top of other cryptographic systems such as Ethereum. in December 2017, the popular game CryptoKitties slowed the Ethereum network and exposed the vulnerability of public blockchains to traffic slowdowns. Decentralized applications use Smart Contracts to connect to a blockchain, where the backend of the Dapp runs on a decentralized P2P network.