This is a good upcycle as well as a good technique for growing your own veggies when the weather may still be a bit cold -- Cold frame window. Helps you grow vegetables and plants earlier at spring. Good re-use for those old windows!
mini greenhouse, would start plants sooner in the spring and protect from frost. Would also be good to cover short plants to protect from hard rain. It would be even better if the windows either folded flat to the side or came off entirely.