MatWM 2

matwm2 is a simple window manager for X11. It features window frames with titlebar and buttons, configurable key bindings and mouse buttons, support for EWMH and motif hints, focus-follows-mouse and click-to-focus focus models, virtual desktops, Xft fonts and xinerama support.

It is written in C, it is mostly valid ISO C90 but uses several libc functions and system calls not specified by the ISO C90 standard (setenv(), waitpid(), and either vfork() or fork() (these are specified by the POSIX.1-2001 standard) - forgive me if i forgot one).