What the hell is decentralized finance?

Fervent proponents of cryptocurrencies and the blockchains they run on have promised a lot. To them, these technologies represent salvation from corporate power over the internet, government intrusions on liberty, poverty and virtually everything else that ails society. But so far, the reality has mostly involved financial speculation with popular cryptocurrencies like bitcoin and dogecoin, which soar and plunge with alarming regularity. So what are cryptocurrencies and blockchain good for? As