X window manager

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An X window manager is a program that runs on top of the X Window System, which is used on Unix-like systems. Unlike Windows or macOS, the X system separates the display server from the window manager, so you can choose from many different managers.

What a window manager does
- When you open a new window, the WM decides where it appears and how it looks (borders, title bar). It also handles moving and resizing by mouse.
- Icons aren’t part of the core system; the WM creates and manages them.
- The WM can also handle things like clicks on the desktop, startup actions, and keyboard shortcuts.

Communication with applications
- Window managers talk with applications using standard protocols. The original protocol was ICCCM, but today most use Extended Window Manager Hints (EWMH). These let apps set window titles, decorations, whether a window is minimized, and which virtual desktop it belongs to.

Types of window managers
- Stacking (traditional): windows are drawn one over another, so they can overlap. This is fast but doesn’t support translucency.
- Tilting: the screen is divided into non-overlapping frames, so windows do not cover each other. Examples include i3, dwm, xmonad, awesome, and others.
- Compositing: each window is drawn to an off-screen buffer, then all buffers are combined on the screen. This enables effects like shadows and translucency but uses more resources. Some WMs can run with a compositor to add these effects.
- Virtual desktops: some WMs use virtual screens, letting you have more windows open than your monitor could show at once. Examples include FVWM and Tvtwm.
- Extensibility: many WMs can be customized or extended with scripts to add new actions or change how they respond to events.

Examples
- Stacking: AmiWM, Blackbox, CTWM, Enlightenment, Fluxbox, FVWM, IceWM, MWM, Openbox, TWM, Window Maker.
- Tilting: awesome, dwm, ion, i3, xmonad, wmii, ratpoison, StumpWM, (and others).

Special note
- You can add a compositor to a non-compositing WM (for effects like shadows) using a separate program such as compton.

In short, an X window manager gives you control over how windows look, where they appear, and how you interact with them, while offering many different styles and levels of customization.