Gabriel Nicholas at Wired:
… it is a new type of distributed computer—one that no one controls but inside which anyone can see. On this computer, a new generation of applications, called ‘DApps,’ is being born….
Decentralized apps, or DApps, are programs that run on the world computer. “Run,” however, might not be the right word, because Ethereum-the-computer is dreadfully slow, and writing code for it is like turning back the digital clock a few decades. Computation on the EVM right now is far too expensive and inefficient to run a modern web-based service like Twitter. Storing even a single profile picture would cost hundreds of dollars, and today the network can only run about seven transactions per second. (For comparison, Facebook runs 25,000 transactions per second on searches alone.) Software changes can speed things up some, but Ethereum is always going to be slower than more conventional computing.
It’s a cumbersome system, but that’s not deterring developers from writing Ethereum programs. They’re attracted to what the platform earns by spending all those extra resources. DApps are small, interconnected scripts that transfer currency and connect users. They are good at coordinating lots of computers to perform tasks in exchange for currency without any central oversight. This decentralization is Ethereum’s biggest draw. DApps do not need to trust in the benevolence of central administrators like Amazon to run code, or in payment systems like PayPal or banks to exchange currency.
Blockchain theorists have a name for this decentralized protection from outside meddling: They call it “trustlessness,” and it is at the core of many DApps. (The term is confusing, because it sounds like a label for something you can’t trust. But what it’s really saying is, because you can trust the cryptography and the blockchain, you don’t have to take anyone’s word for anything.) The “Hello, World!” of Ethereum DApp development—the starter exercise programmers use to learn how a system works—is a voting DApp. If a voting DApp were used in say, a presidential race, the DApp could autonomously count the votes and determine a winner. All votes would be anonymous, but anyone could see the code that counted them and the system would be immune to meddling from, say, Russian oligarchs.