Published by Chris Coyier
Project from Matt Wilcox for serving the right images to the right devices (i.e. small images to small browser windows, large images to large browser windows). Small browser windows, regardless of bandwidth considerations, shouldn't get a giant image scaled down they should get an image just the size they need it.
This is similar to an earlier project by the Filament Group, but this takes more of a "just works" approach in that it doesn't require you to do anything special or even create the different versions of the images yourself.