The concept album is #filk music to public domain #hymn tunes, as a way to explore copyright. The premise is that a lonely space traveler is wondering what he'll find when they get to his destination, and due to copyright restrictions the only media they have with them is public domain (mostly before 1923) so he combines the two. While every song relates to one or more fandoms, they've all had the clear identifications scrubbed, (because of copyright, trademark and brand dilution -- which fits with the theme). Also, some of the songs are related to relatively obscure books.
The album will be released with a #CreativeCommons Attribution license and will include full sheet music. This means folks can take the sheet music and perform the songs for profit to live crowds or create a derivative of the song and add it to their album. The hymns came from MusicXML and ABC sources, but #Lilypond is nice enough that we standardized on that.
When the album is released, we're thinking of posting the source to Github so that folks can fork it. The organization we're using allows the files to be compiled in different ways as it isolates music, lyrics, and format in to three different files. We like it well enough, that we're planning to use a similar approach for the Christmas 2015 stuff. (If we're lucky we'll release the Christmas 2015 stuff with full sheet music this year.)
It is getting pretty exciting. We're reaching a point where we're actually thinking of beta readers for the song book.