What are some alternatives?
When comparing Tombstone Engine and PaperWM, you can also consider the following products
Armory3D - Armory 3D is a free and open source game development software developed using Haxe and Kha and made to run inside Blender.
i3-gaps - i3-gaps is a fork of i3wm, a tiling window manager for X11.
bspwm - A tiling window manager based on binary space partitioning
Panda3D - Panda3D is a video game development engine and rendering software. It is developed and maintained by the Carnegie Mellon University Entertainment Technology Center.
dwm - 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.