Notion is a tiling tabbed window manager for X. This means the screen can be freely divided into tiles that contain the client windows. Multiple client windows can occupy the same tile; in that case they will be tabbed, much like browser tabs. This way, windows will not overlap and it becomes easier to manage your screen real estate. Its functionality can be configured and even extended with Lua scripts. Various scripts are available, such as for NetWM features and multihead support.
Lunchbox is a dynamic tiling window manager for X11. It allows windows to be resized by squishing them against the edge of the screen. In a step away from the desktop metaphor, all programs are given a separate workspace and unique arrangement of windows, and any window can become the desktop. It offers an in-built scalable tab replacement called the Title Menu, which allows any window to be swapped with any other window that fits, allowing very fine grained control over the layout of the screen. Finally, although many windows default to tiling, any window can be changed to a Floating mode, which dialog boxes default to.