Slider is a classic game played on a grid of tiles that has one tile missing, making an empty space. The numbered tiles may be moved around by sliding them into the empty space. The object is to sort the tiles in numerical order, so that the '1' is in the upper left, the '2' just to the right, and so forth, with the empty space in the lower right.
You can select from a number of puzzle sizes. Obviously the smaller puzzle sizes are easier to solve than the larger sizes.
You can save your game by bookmarking the page in the game you want to come back to later. This works for all pages of the game except for the first (which has "newgame" in the URL), so if you want to bookmark a particular puzzle from the beginning, you have to make at least one move first.