Build a Hard Drive Clock - a Hard Disk that tells time
"Have an old hard drive that no longer works? As long as it still spins up chances are you could build a clock out of your old hard drive!". That's right, here's way to finally put those old megabytes to use. It requires a bit of electronic experience, but it's a pretty cool thing to build. Here's a video of it working.
Get the schematics and other details from here