DAO stands for "Decentralized Autonomous Organization". Mostly live on Discord servers, these are groups of strangers on the internet who trust the governance of their organization (key decision making) to a program as a smart contract. Think of programmed trust - instead of trusting organizations of people, you can trust that the code will execute the decision making as promised. As usual, an overview first.
This is a primer with a compilation of interesting articles. Dig in if you want the ultimate resource.
Below are interesting applications of DAOs so far.