Otter Browser is a full-featured Qt desktop web browser written in C++, aiming to recreate the classic Opera 12 user experience. It is an application codebase, not a data/research repository. The code implements tabbed browsing with bookmarks, history, sessions, feeds, password management, content/ad blocking, cookie controls, downloads, spell checking, and import/export for HTML, XBEL, Opera, and OPML formats. Architecturally it is a modular Qt monolith: a core layer of singleton managers (SettingsManager, BookmarksManager, NetworkManagerFactory, ActionsManager), a large custom UI layer, and pluggable backends for web rendering (QtWebEngine and legacy QtWebKit), platform integration (Windows, macOS, FreeDesktop), and password storage. Entry points are src/main.cpp, src/core/Application.cpp, and src/ui/MainWindow.cpp. Data flows are primarily local and browser-centric: user configuration and browser data are persisted as JSON, INI, XML, and XBEL files, while network requests flow through NetworkManager, CookieJar, and NetworkCache. External dependencies include Qt 5.15+, QtWebEngine, OpenSSL, GStreamer, and Hunspell. The main technical debt is the legacy QtWebKit backend, vendored older third-party libraries (Breakpad, Sonnet), and incomplete Qt5/Qt6 compatibility shims. Overall, the codebase shows solid professional Qt engineering with several cleanly separated reusable widgets and parsers, but is held back by singleton-heavy design and some stale components.