I saw something (I forgot where, and what's it called) that's a little switch that you put on your tuner, you flick it and it gives your string an extra something of length, or shortens your string to give you a higher/lower pitch. This can't be very good for you neck, or string or...probably anything, but sounds like something cool to do. Maybe you're doing a completely solo thing, then you wanna drop your E to a D, just flick the switch, play, then when you're going back to original tuning, just flick the switch back.
It was also really expensive, if I remember correctly.
edit: Here we are: [Invalid or Expired Link Removed]
^that page is cool. Has bass tremolos too!