This app was mentioned in 2 comments, with an average of 1.50 upvotes
Just FYI there is another app that does exactly this and is a little slicker to use in my opinion: https://play.google.com/store/apps/details?id=de.daniworm.schattenwurf (name is German, interface is in English)
I'm partial to SchattenWurf on Android due to the minimalism and ease of use. It does what it needs to and does it well.