Easy, Classic and Expert
While you can choose every last rule exactly as you want it (which would make it "custom" settings), we've also selected commonly picked choices for games under the Easy, Classic and Expert groups. Some games don't have as many settings (for instance, Clock) so there isn't always an extensive option for this.
In the case of Klondike, Classic would be very similar to the default settings of the Solitaire app that used to be bundled with Microsoft Windows.
We've also added Easy settings which make it a far more relaxing game, or ideal for kids.
The Expert settings are usually for more advanced players, and typically will be more difficult and unlikely to lead to a winnable game!