Resurrection is a modification for Fallout 2. It has a completely new story and takes place in New Mexico, sometime between the events of Fallout 1 and 2. It's as if there had been a third classic Fallout game.
One of the slickest, most professionally made mods I've had the pleasure of playing. It's one of those rare mods where you can almost forget you're playing a fan-created work, so seamlessly does it hit all the checkboxes for a studio created game. It's right up there with Black Mesa in that regard.
For Fallout fans wishing for another classic, this is your dream come true. Get it and play it - you won't be disappointed.