i3 is an improved dynamic tiling window manager.
Key features of i3 are correct implementation of Xinerama (workspaces are
assigned to virtual screens, i3 does the right thing when attaching new
monitors), XrandR support (not done yet), horizontal and vertical columns
(think of a table) in tiling. Also, special focus is on writing clean,
readable and well documented code. i3 uses xcb for asynchronous
communication with X11, and has several measures to be very fast.
Please be aware i3 is primarily targeted at advanced users and developers
and that you're currently trying an alpha version (which may contain bugs).