Note: Development for EDDS has stopped. Dr. Kaii's excellent EDProfiler tool does all that EDDS did and much more (link).
EDDS allows you to change graphics settings before running Elite: Dangerous. Especially useful if you switch between Oculus Rift and regular monitor, or if you switch display settings often for any other reason. It also lets you change GUI color, as well as enable a second window on your monitor for OR use.
EDDS is now hosted on Biobob and Wolverine2710s excellent EDCodex. Go here for description and download:
EDDS at EDCodex