I bought a super-cheap-on-clearance set of fabric paints for a couple bucks. We used the paint for a birthday party craft but had some left over.
(The project was "paint your own hats." It was fun AND served as a parting take-away for the guests. Just say no to goodie bags.)
One of the party guests suggested we could use up the paint by making window clings. Turns out, if you paint designs on wax paper using fabric paint, once dry you can peel them off and stick them to the window!
A couple days later, my daughter tested this theory and the results are pictured above.
Hers are simple freehand designs on wax paper, but you can also slide a line drawing into a plastic sheet protector and paint over it. You can also create marbled or stained glass effects by swirling the paint colors together with a toothpick.
Fun, quick diversion for summer and for Christmas or Halloween window decor.