From ThisBlueWiki
The most retardedly obvious fucking idea on the planet, and nobody has written a (good) version yet that I can find.
A shell extension for 'doze which copies files, not overwriting ones that don't need to be overwritten, not dying on errors (such as invalid filename on target filesystem), and so on. Come on. Why doesn't this exist? Why isn't it part of the shell by default? As a bonus, add hash verifies. :P
See also: Totalcopy, Robocopy.