Decman is a declarative package and configuration manager for Arch Linux that ensures system state matches user-defined specifications. It uses a modular architecture with a core application and plugins for managing different subsystems (pacman, AUR, systemd, flatpak). Users define their desired system state in Python files, and Decman executes these specifications to install/remove packages, manage files and directories, enable/disable services, and apply other system configurations. The system tracks its state in a JSON store to determine what changes are needed between runs, and provides hook functions for custom logic at various points in the execution lifecycle.