Dagger is a platform that enables developers to create self-contained project environments with all dependencies installed, regardless of operating system. It uses a modular approach to build pipelines, allowing for reusability and extensibility. Mark Sági-Kazár, Head of Open Source at OpenMeter, has successfully implemented Dagger in his company's production pipelines, eliminating the "push and pray" problem, inconsistent environments, onboarding friction, and lack of reusability. He uses Dagger Functions and Dagger Cloud to manage testing, releasing, and deploying processes, resulting in maximum satisfaction for both developers and platform engineers. Mark attributes Dagger's success to its ability to write pipelines in a language known by the developer, creating a self-contained environment that minimizes time waiting and maximizes productivity.