These games have the unique property that the four rightmost columns on the tableau (the "rank columns") build in like-rank. All four variations are free-to-play. No in-app purchases.
In RELAXED games an empty rank column will accept any card. In STRICT empty rank columns cannot be filled.
WILLOW - Build the tableau (first seven columns) in alternate color suit.
STILIO - Build the tableau (first seven columns) in mixed suit, but group moves are only allowed for sequences of matching suit.