It seems that wmctrl is not installed on my system (Mac OS 10.8), but when I try to install it by cloning a git repo and following the instructions (./configure, make, make install), running make results in a bunch of errors, the first few of which look like this:
main.c:33:22: error: X11/Xlib.h: No such file or directory
main.c:34:23: error: X11/Xatom.h: No such file or directory
main.c:35:28: error: X11/cursorfont.h: No such file or directory
main.c:36:29: error: X11/Xmu/WinUtil.h: No such file or directory
Does the wmctrl directory need to be somewhere else?