They are both file sharing programs. They are basically the same thing, LimeWire was shut down officially and FrostWire took over. FrostWire just found all the right loop holes and knows what they are doing legally to keep from being shut down. The creators claim the only purpose for the program is to share a file between two friends. Like if I wanted my brother to watch a video I made I could upload it to FrostWire and he could download it and watch it, that easy. Obviously there is no way to tell if the person uploading the file owns it or not so people upload their music that they have either gotten off of a cd they actually bought or from an online store. The music gets uploaded and people from anywhere in the world can download it. The cycle just keeps going. You can see the controversy here. The site covers themselves by making you agree that you won't use it to share files you don't own before you install it, after that it's on you if you do it or not. There have been instances where people were tracked down and forced to pay a lot of money for all of the music they stole but the industry has since basically given up on everyday people downloading a couple of songs so there is not really that much risk involved.