SpecTrek was among the winners of the Android Developer Challenge II and that's what brought my attention to it. I've been trying to work my way through the winning apps that are actually available to us, and this one is clearly among the most innovative.
It clearly takes a page out of geocaching's book, but instead of finding real, hidden stashes of 'treasure' you're ghost hunting just like in the movie Ghostbusters. Your Android device becomes both your ghost finder and your weapon in capturing the specters.
First, you pick how long of a game you want from a short 15 minute game to a long 2 hour game. The length of the game determines how far away and how many ghosts there will be to catch. Once that's done the imaginary ghosts are placed and it's a race to find them. Consequently, this doubles as a fitness game as you walk or run to set a record time for finding and capturing ghosts.
Obviously if you don't want or like to walk around then you won't find any love for this game. Likewise, you might not get your thrills off of capturing things that don't really exist and prefer to stick to traditional geocaching. However, this doesn't require people to have placed caches for you... is a nifty family game or solo game that gets us out of the house... and the kids seem to love it.