Homebrew is a mature, cross-platform package manager for macOS and Linux implemented in Ruby. It provides command-line tools for installing, updating, and managing software packages (formulae) and GUI applications (casks). The architecture features a modular design with clear separation of concerns, including command patterns, strategy patterns for download/unpack operations, OS abstraction layers, and DSLs for package definitions. Key entry points include the brew executable, cmd/ directory for user commands, and dev-cmd/ for developer tools. The system handles dependency resolution, binary package distribution (bottles), tap repositories, Brewfile dependency management, analytics tracking, and service management. External dependencies include system tools (git, curl, compilers), Ruby runtime, and various external services for version checking and vulnerability scanning.