I first saw Twine several months ago, but for some reason, it didn't stick. It's a tool for making interactive fiction (games, choose-your-own-adventure stories, that kind of thing).
I heard about it again recently and am starting to put a game/adventure together. I've had a big project in mind that I submitted for Creative Capital--a mix of role-playing games, walking tours, poetry and naturalist observation. They turned it down, and then the master naturalist program turned it down. But I don't care. It's stuck in my brain and I'm going to work on it. And Twine, I think, is the right tool for the job.