FastFret?
I don't use the stuff very often. A guy actually gave my the one I have. It's like roll-on for your strings. I don't know if it's alcohol or some kind of oil. It does work to get the crud off the bottom of strings when they've been sitting around a while. I don't like the greasy feel afterward, so I wipe them down pretty good afterward.
My strings don't usually get to the month old mark before I've changed them. But every once in a while I get out some old guitar I don't gig with that's all crudified. Especially my acoustic. Those strings are so old, they are deformed around the frets.
Acoustic strings suck, don't they? They are way too jangly when you first put them on, then they go deader than shit after you play them for an hour. Here's an appalchian trick if you like the jangly strings on your acoustic. When I put strings on, I tune it up to like C and play until they're dead. Then tune them up to D and play them till they're dead. Then tune them to E. It's like getting 3 sets for the price of one.