While it's not Saturday anymore, I've got a fun, free app for you. It's sorta math related in that you have to figure out some balance/architectural issues as you go...
On DropBrick Christmas you need to clear boxes below Santa in order to have him land safely on the platform below. I was reminded of how entertaining this can be when we sat through a two-hour-plus music concert last night without an intermission. My 8yo and I played it a lot! ;)
Looking for more free, fun, education-related apps? Check out the entire series.