bug.n is described as 'Tiling window manager add-on for Microsoft Windows. It is written in the scripting language AutoHotkey' and is a Window Manager in the news & books category. There are more than 50 alternatives to bug.n for a variety of platforms, including Linux, Wayland, Windows, Mac and BSD apps. The best bug.n alternative is Hyprland, which is both free and Open Source. Other great apps like bug.n are Noctalia, niri, Sway and i3.
Emerge Desktop is a replacement Windows "shell" (the desktop environment normally provided by Windows Explorer) for Windows 2000 and above. In order to replace Windows Explorer as a shell, it provides a system tray (the area that collects the icons collected at the...
xmonad is a dynamically tiling X11 window manager that is written and configured in Haskell. In a normal WM, you spend half your time aligning and searching for windows. xmonad makes work easier, by automating this.
The Emerald Theme Manager allows you to install, edit and switch between Emerald themes. In order for it to work, select Emerald as your window decorator. You will also need to enable the Window Decorations plugin (via CCSM).
spectrwm is a small dynamic tiling window manager for X11. It tries to stay out of the way so that valuable screen real estate can be used for much more important stuff. It has sane defaults and does not require one to learn a language to do any configuration.
SharpEnviro (or SharpE) is an open source shell replacement system for Microsoft Windows XP, Windows Vista and Windows 7. When using SharpEnviro the default Windows desktop is replaced by a new and more powerful desktop environment.
BB4Win (Blackbox for Windows) is an alternative shell for Microsoft Windows. The program aims to emulate the look and feel of a Linux based desktop. The BB4Win project was discontinued in 2005 but various branches have been built from the source.
wmii is a small, dynamic window manager for X11. It is scriptable, has a 9p filesystem interface and supports classic and tiling (acme-like) window management. It aims to maintain a small and clean (read hackable and beautiful) codebase.
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NERD tree has absolutely nothing to do with desktop window management, and should never have been listed as an alternative.