Sloppy focus

Sloppy focus or focus follows mouse is a desktop navigation paradigm that originated on Unix systems. It has the advantage of needing less clicking, and, when clicking is set to not raise the active window, can allow input to windows that are not on top. a

KDE4

In System Settings, choose the Window Behavior dialog. Under the Focus tab, set the Policy to be Focus Follows Mouse and uncheck the Click raises active window box. To raise a window, use alt+tab or click on the titlebar.