Line 6 is a California based company who create various gadgets for guitarists. They first came about in the mid 90’s with the AxSys guitar amplifier, and their product line has expanded to include effects pedals, software and guitars.
What sets Line 6 apart from their competitors is their reliance on digital technology; they were not the first company to explore digital modelling but they were the first to aggressively market it. All line 6’s products use digital processors to emulate famous equipment - their amplifiers claim to be able to produce any sound from roaring Marshall stack to a fender twin reverb. Their guitars are supposed to change from Gibson crunchiness to Fender jangle at the flick of a switch, though I’ve always wondered how they are able to get away without getting sued when they reference and copy their competitors' products so explicitly - presumably their lawyers know just how far they can go.
The main problem they face is that many guitarists are natural luddites and audiophiles who abhor any piece of equipment that is not analog - consider that the most popular guitar in the world is a 40-year-old design. Opinions vary on how effective this stuff actually is but at the moment it is hugely popular. It's easy to see why when you consider the cost of buying and maintaining a collection of wonderful guitars and amps versus the price of a little digital bean.
Personally I find digital modelling is incredibly useful for home recording - it’s extremely hard to tell the difference on a recording between a “Fake” amplifier and a real one, although I do find the idea of a digital acoustic guitar indefinably creepy.