The Brainstormer is an iPhone and iPad app for $1.99 that lets you spin a wheel to randomly combine words to create a plot with a subject and a setting or style. Of course most of them are not really usable, but they are fun and can stimulate your thinking. Here is one I just did:
Odd Couple +
retro sci-fi +
Hmmm….maybe a comedy variation of "The Portrait of Dorian Grey" in which an obnoxious "star'" artist who paints pictures of space suddenly finds himself whisked into an alternate reality in which he is at the mercy of someone very much like himself… Well, I did say most are not really usable!
Make your own analogue version
You can make your own by creating lists or a batch of index cards with types of characters, settings, genres, and emotions.
Randomly take one from each stack or list and see how they could fit together into a story.
Great for when your creative mind feels sluggish. Have a few minutes of fun with this before starting on your project.
(Want to find out how to be more creative? The answers are in my book, "Creativity Now," published by Pearson and available from Amazon or your other favorite book seller.)