Sea Towers Solitaire is one of the many 'cell' related variants where there are one or more 'free cells'. The purpose of these are as 'storage' to allow you to place cards temporarily. This in turn helps you arrange the Tableau in the required order.
A good game, but perhaps a little easy (although less so then the great Free Cell itself).
Big Free cell, Free cell, Forecell, KingCell, Sea Tower, Seven by Four, Six by Four, TwoCell.