What It Is
This is the description from the official
website:
LilyPond is a music engraving program, devoted to producing the highest-quality sheet music possible. It brings the aesthetics of traditionally engraved music to computer printouts.
LilyPond is a free, open-source software package that lets users create awesome looking sheet music. Though it won't cost you any money, be prepared to spend some time learning how to use this program. All input is done through text files, not GUI's like in commercial, high-end software.
Why do I care?
First of all, IT'S FREE. That's got to be a good reason to care. Sure, I'd like to have a copy of Finale, but that costs $120 for the sheet music software, with the full package at $600! I'm a grad student, so that money is all spent on ramen and coffee. So learn something new and save some money.
Though this can be harder to learn, it can be much faster to input once you learn the system (assuming your don't hen peck your keyboard). Each note can take from one to five characters to enter, in general. With practice, you will be able to get a first draft out in no time.
The last, and arguably the best, reason: the output looks great. The developers put in a ton of effort so that you don't have to. They provided a lengthy discussion about the by-gone days of hand engraving, and the poor replacement that computer generated music has been
here.
Go check out LilyPond and start making music!