Lerna is a monorepo management tool for JavaScript/TypeScript projects that provides CLI commands for versioning, publishing, and managing multiple packages from a single repository. It features a modular architecture with separate command implementations, core utilities for project graph construction and dependency resolution, and integration with Nx for task caching and distributed execution. The tool supports both fixed and independent versioning modes, conventional commits for automated changelogs, and works with multiple package managers (npm, yarn, pnpm, bun).