spectrwm is a small, dynamic tiling and reparenting window manager for X11. It tries to stay out of the way so that valuable screen real estate can be used for much more important stuff. It has sane defaults, and it does not require one to learn a language to do any configuration. spectrwm is written by hackers for hackers and it strives to be small, compact, and fast.
spectrwm was largely inspired by xmonad and dwm. Both are fine products, but they suffer from things like: crazy-unportable-language syndrome, silly defaults, asymmetrical window layout, the 'how hard can it be?' (to code efficiently) problem, and good old NIH. Nevertheless dwm was a phenomenal resource, and good ideas and code were borrowed from it. On the other hand, xmonad has great defaults and key bindings, plus xinerama support, but it is crippled by not being written in C.