this was really popular in the 70's.

Regular or Lower calorie cool whip carton,
2 cartons of yogurt (lemon or lime worked well)Stir all together, pour in a premade graham cracker crust.
Let it set up overnight (invert the plastic lid that came on the pie crust as a cover)
If you keep crushed graham crackers around, sprinkle some on the top.
SO easy to make.