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, Windows, BSD, Mac and KDE. The best alternative is i3, which is both free and Open Source. Other great apps like bug.n are Cairo Shell (Free, Open Source), Openbox (Free, Open Source), VirtuaWin (Free, Open Source) and awesome (Free, Open Source).
StumpWM is a tiling, keyboard driven X11 Window Manager written and scriptable in Common Lisp. StumpWM attempts to be customizable yet visually minimal. There are no window decorations, no icons, and no buttons.
PaperWM is an experimental Gnome Shell extension providing scrollable tiling of windows and per monitor workspaces. It's inspired by paper notebooks and tiling window managers. Supports Gnome Shell 3.28 and 3.30 on X11 and wayland.
Windawesome (pronounced - contrary to what you would expect from the way it is written - Windows-om, not Wind-awesome) is a highly customizable tiling/dynamic window manager with multi-monitor support for Windows, which works on top of explorer.exe and not as a shell replacement.