sisctrl is a gtk-2.x based tool for the XFree86/X.org SiS ("sis")
driver to tune the display parameters during X server run-time. Among
other features, it allows switching and changing output devices, tuning
TV output, gamma correction and Xv (hardware video) properties. It also
supports  switching the display mode and resizing the desktop using the
RandR extension.

WWW: http://www.winischhofer.net/linuxsisvga.shtml#23