DisplayCAL (formerly known as dispcalGUI) is a display calibration
and profiling solution with a focus on accuracy and versatility
(in fact, the author is of the honest opinion it may be the most
accurate and versatile ICC compatible display profiling solution
available anywhere). At its core it relies on ArgyllCMS, an advanced
open source color management system, to take measurements, create
calibrations and profiles, and for a variety of other advanced
color related tasks.