I just downloaded this app and its perfect for what I wanted. There are a ton of apps that will work for standard tuning a guitar. I needed an app that would work for alternate tuning and I figured a piano tuner would be able to tune to any note there is to play. And it did. Naturally, you have to know the note you want to tune the string to. If you dont know what drop-D or drop-C each string needs, then you might need another app, but if you know what you want to tune each string to, this is perfect.
Llyrin about Pano Tuner Lite