Six different types of pieces and as in the original three or more pieces in a row are deleted and new fall down from the top. You tap-drag to switch places with a neighbor, and the drag is indicated by a slight move of the piece your holding on to in one of the 2-4 possible directions. Works with mouse, and is instantly portable to iOS without any extra code.
Slap a few levels and some design in there, then it's just to get someone to write you that $6,000,000,000 check.
