Ratpoison is a simple Window Manager with no fat library dependencies, no fancy graphics, no window decorations, and no rodent dependence. It is largely modelled after GNU Screen which has done wonders in the virtual terminal market.
The screen can be split into non-overlapping frames. All windows are kept maximized inside their frames to take full advantage of your precious screen real estate.
All interaction with the window manager is done through keystrokes. ratpoison has a prefix map to minimize the key clobbering that cripples Emacs and other quality pieces of software.
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Pro Simple config file
Ratpoison is simple to configure as a window manager. In fact, it doesn't necessarily require that much configuration as it is so simple in structure to begin with.
Pro Very little mouse interaction.
Ratpoison is designed to be mainly used with a keyboard and keybindings, making mouse interaction unnecessary.
Pro Support for multiple desktops
Ratpoison offers support for multiple desktops through the use of the rpws script.
Pro Good online documentation
Ratpoison has plenty of documentation (to be found online) on how to operate and configure the window manager.
Con Might make some games crash at startup
Con Does not work well with applications that have multiple windows
Being that Ratpoison is a tiling only window manager, trying to use applications that have multiple windows (such as GIMP) becomes a PITA.