Notion is an X11 window manager with tiling, tabbing, and floating layout capabilities. It features a modular architecture where core functionality resides in ioncore/ and extends via loadable modules (mod_tiling, mod_menu, mod_statusbar, etc.). Configuration and extensibility are driven by Lua scripts, allowing deep customization of key bindings, layouts, and status bar elements. The system handles X11 events, manages window geometry and focus, and provides session saving/restoring. Key components include a reference-counted object system (libtu/obj), Lua-C binding layer (libextl), hook system (libmainloop/hooks), and binding maps for contextual input handling. Despite its age, the codebase shows recent activity and maintains compatibility with modern X11 environments.