OpenCart is a free and open-source e-commerce platform written in PHP. It provides a complete online store solution with both a storefront (catalog) and an administrative backend. The architecture follows a custom MVC framework with a route-based dispatch system, event hooks, and an extension system for payments, shipping, modules, and themes. The frontend uses a mix of jQuery (admin) and a custom WebComponent framework (catalog) with a custom template language called Curlytag. The system supports multi-store, multi-language, and multi-currency out of the box, with background task processing for cache generation and email delivery. In production, OpenCart handles product catalog management, shopping cart and checkout flows, customer accounts, order processing, payment integration, shipping calculations, tax handling, and reporting. It includes CMS capabilities (articles, blogs, comments), GDPR compliance tools, and SEO-friendly URL rewriting. The admin panel provides full control over store settings, localization, user permissions, and extension management. Key entry points include the storefront index.php (catalog), admin/index.php (admin panel), and system/framework.php (application bootstrap). External dependencies include a database (MySQL/PostgreSQL), optional caching (Redis/Memcached), and third-party libraries for email, template rendering (Twig), and code editing (CodeMirror). The system is designed to be extensible through a plugin architecture that allows adding new payment gateways, shipping methods, and frontend modules.