The closest window manager that has a similar ability to compiz & dim-inactive is kde's kwin.
A couple of screen-shots will help here - both showing kwin running in xubuntu:
kwin running without dim effect
kwin running with dim effect
If disk-space is not an issue for you (150Mb+ install) then kwin can be installed as per this Q&A:
To run kwin use the following:
nohup kwin --replace &
Launch the KDE Control Module as per:
Then enable and configure Dim Inactive effect:
tip if you don't like the "glow" effect then turn it off in window decorations - Configure Decoration - Shadows and untick the active window glow check-box.