OpenGrok is a production-grade source code search and cross-reference engine, written primarily in Java with supporting Python tooling. It indexes source code repositories from multiple version control systems (Git, Mercurial, Subversion, Perforce, CVS, RCS, SCCS, BitKeeper, etc.) and provides a web-based interface and REST API for searching, browsing, and annotating code. The system is architected as a Lucene-backed indexer (opengrok-indexer) that analyzes source files using language-specific JFlex lexers and ctags for symbol extraction, a web application (opengrok-web) built on Jersey and Jakarta Servlets, a suggester module for autocomplete, and a plugin-based authorization framework supporting LDAP and header-based authentication. Key entry points include the Indexer CLI, the web application's REST controllers (e.g., SearchController, FileController, HistoryController), and Python administration scripts (opengrok-indexer, opengrok-mirror, opengrok-sync). External dependencies include Apache Lucene, JFlex, Universal Ctags, and various VCS binaries. The codebase demonstrates strong engineering practices with extensive unit and integration tests, Docker deployment, and a modular analyzer hierarchy covering over 30 programming languages.