This isn't exactly an app or traditional tuner, but I recently put a TronicalTune unit on one of my guitars (Les Paul Studio -- it's my project guitar) and it's the coolest thing I've ever played with: http://www.tronical.com/ Makes it so easy to switch tunings, the locking tuners are great (learning to string it up properly takes some time, but it's worth it), and it doesn't add too much weight to the headstock. Can't recommend it enough for guitarists with compatible equipment; really wish they'd make one that would fit on my 8-string or my PRS!
(Note: Not affiliated with them in any way, just become a huge fanboy lately!)
Ouch, they cost more than most of the guitars I own (Epiphone makes really decent stuff these days, acoustic and electric). Definitely cool tech, though.
Pretty cool. Did you have to drill out the headstock, or did it fit the tuner holes? I'm a bit vary of putting power tools to my Les Paul.
And how does the weight feel? I put Planet Waves Auto Trim locking tuners (also highly recommended, btw) on my project Strat, and it became noticeable top heavy.
I didn't have to drill anything at all -- fit perfectly. Just make sure you print out the template first and check it. The install took me all of maybe 5 minutes; it took me longer to figure out how to calibrate it for the first setup than to actually get the thing on the guitar (protip: read the manual first ... I didn't).
I don't notice any difference whatsoever from the Hipshot locking tuners I put on there previously. However, this particular guitar is slightly insane, weight-wise; two heavy magnetic pickups with metal cases, piezo bridge and preamp, GK-3 MIDI pickup. It's chambered, but weighs more than an unchambered LP Custom, due to all the extra equipment. So the headstock doesn't exactly add much.
(Note: Not affiliated with them in any way, just become a huge fanboy lately!)