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.
DSWM (Deep Space Window Manager) is a tiling keyboard-driven X11 window manager. It is based on StumpWM code and is written entirely in Common Lisp and oriented for good usability with minimum startup configuration and good integration with Emacs. The project is under hard development, so it has many experimental features.
euclid-wm is a minimalist tiling window manager for X11. It is designed to allow quick and easy management of numerous windows entirely from easy-to-learn, Vim-like key-bindings. It seeks to do two things in particular: balance the ease of use common among automatic-layout tiling window managers with the flexibility of manual layout window managers, and create a useful way to handle minimized applications.