If you don't have a garage I hope you at least have a warehouse or a barn loft or whatever Kevin Bacon was using in Footloose. Similar to as seen on TV workout! (Side note- I once bought my mom a gift that was labeled "Similar To As Seen On TV"). Didn't have the cash for the As Seen On TV gifts.
Each corner will have its own exercise and then the middle will be an exercise as well. So here is how to set it up.
Corner 1-Jumping jacks
Corner 2-Cross country ski
Corner 3-Punches
Corner 4-High knees in place
Middle-Jump ropes (or the invisible jump rope)
You do 60 seconds in corner 1, go to 30 seconds in the middle, 60 seconds in corner 2, 30 seconds in the middle, 60 seconds in corner 3, 30 seconds in the middle, 60 seconds corner 4, 30 seconds in the middle. Go as hard as you can on every exercise, the whole circuit will take you 6 minutes. Then rest for 2 minutes. Repeat the circuit 2 more times for a total of 3 times all the way through. The whole workout will take 22 minutes and it can be hard (or easy) as you make it.