Spectrwm is a small dynamic tiling 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 does not require one to learn a language to do any configuration. It was written by hackers for hackers and it strives to be small, compact and fast.
It was largely inspired by xmonad and dwm. Both are fine products but suffer from things like: crazy-unportable-language-syndrome, silly defaults, asymmetrical window layout, "how hard can it be?" and good old NIH. Nevertheless dwm was a phenomenal resource and many good ideas and code was borrowed from it. On the other hand xmonad has great defaults, key bindings and xinerama support but is crippled by not being written in C.