i3 is a dynamic tiling window manager with clean, readable and documented code, featuring extended Xinerama support, usage of libxcb instead of xlib and several improvements over wmii.
Sway is a tiling Wayland compositor and a drop-in replacement for the i3 window manager for X11. It works with your existing i3 configuration and supports most of i3's features, plus a few extras.
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.
dwm is a dynamic window manager for X. It manages windows in tiled, monocle and floating layouts. All of the layouts can be applied dynamically, optimising the environment for the application in use and the task performed.
Fluxbox is a window manager for X that was based on the Blackbox 0.61.1 code. It is very light on resources and easy to handle but yet full of features to make an easy, and extremely fast, desktop experience. It is built using C++ and licensed under the MIT license.