&gt;  I figure I&#x27;ll just ask this here. Why can&#x27;t you use something other than Aqua?<p>Aqua is the default window manager[0] for OS X, so any default OS X applications will be using Aqua-based windows. When I say &quot;focus follows mouse doesn&#x27;t work in Aqua&quot;, I&#x27;m saying that you can&#x27;t get (proper) focus follows mouse behavior on &quot;regular&quot; OS X application windows, no matter what other user-level program you install to handle window management.<p>You <i>can</i> decide to use something that only manages X11 windows (which is what XMonad does), but then you&#x27;re stuck using only X11 applications. (Back when I tried it, even getting an up-to-date X11 build of Firefox on OS X was a pain).<p>[0] I don&#x27;t think the term &quot;window manager&quot; is quite correct here, but since OS X divides things up differently from how Linux&#x2F;X11 work, it&#x27;s the most analogous concept.