subtle is a manual tiling window manager with a rather uncommon approach
of tiling: instead of relying on predefined layouts, subtle divides the
screen into a grid with customizeable slots (called gravities).  For better
understanding, the default config uses a 3x3 grid and maps each gravity to
one key of the numpad.  With those keys, windows can be moved directly to
the desired gravity -- the same can be done with tagging rules in the
config.

Another unique concept is the strict tagging: unlike other tiling window
managers, subtle does not allow weak tagging and always maps windows to
virtual desktops (called views) with matching tags, regardless of the
current active view.