Interestingly Comet Player looks something like a software called Showplay.
As you can see, it's a little more powerful but also $199.
The big difference is you can add your own lyrics or what a musician needs, a chord sheet for backing tracks.
If you could copy and past your own lyric page and save that as a .txt file then you could use the software when it wasn't connected to the web.
For me the chords for a backing track take a format like what follows. If I could paste this into the lyrics screen and then have Comet Player save it with the MP3 file. I'd pay you for that. Now, there are