From the website:

Every songwriter I know keeps a record of the songs they've written. Whether it be in a notebook or on the PC, these songs are usually accompanied by other information like chord progressions, tabs, and sometimes a simple mp3 file. I wanted a way to organize this information myself, and figured there would be a lot of people in my exact situation. With that, the idea for JamJunky was born.
Write songs, send them out and get feedback from your friends and other songwriters, or create a private song vault.