iSeismometer. It showed scrolls of vibrations on the X, Y and Z axes, all at once. None of the newer apps do that. You have to chose a view. I hate that. It's from ObjectGraph LLC, now 404'd.

The original Bejeweled. It didn't want to be Candy Crush, had an endless mode that was perfect for slow adults on subways

Iapetus. The world's tectonic history in three dimensions you could rotate.