ILIAS is a large, modular, open-source Learning Management System (LMS) written primarily in PHP. In production, it provides a full-featured e-learning platform including course management, tests and assessments, surveys, forums, wikis, blogs, portfolios, SCORM content, certificates, chat, and social features. The architecture is a monolithic PHP web application with a component-based internal structure under `components/ILIAS/`. It uses dependency injection (DIC), ilCtrl for routing, a custom UI framework (ILIAS\UI) with factory and renderer patterns, GlobalScreen for top-level UI orchestration, and COPage for rich content editing. Entry points include `cli/setup.php` (installation), `cli/cron.php` (cron jobs), `login.php`, and various web service endpoints (SOAP, WebDAV, REST). External dependencies include MySQL, Node.js (for the chat server), and optional integrations like LDAP, Shibboleth, and LTI. The codebase shows active modernization with PHP 8.3/8.4, strict types, enums, and a structured setup/migration system, though it still carries legacy patterns (e.g., global `$DIC`, old GUI classes) that are being phased out via PHPStan rules and deprecation notices.