"Rap Genius for Code" might be an amazing pitch for avid users of Rap Genius. I wouldn't know. I don't know or care exactly what Rap Genius is, even though I remember there was a recent controversy involving Rap Genius. (It's got something to do with rap music and lyrics? Not my interest.)

If you can explain your site in words that don't require very specific domain knowledge, I think that might broaden appeal.

I think this way of pitching is dangerous for two reasons:

1. Many potential users of the product (Kurikku) will not know about the thing it's being defined in relation to (Rap Genius), and will not understand that they should check it out

2. Those that do know might make a different comparison than you. I might say "It's like Github for music!" and you will think "Oh, so you put in scores and people can collaborate -- just like with code on Github!", but I was thinking "You store your personal music library in the cloud and you can clone it to all your machines -- just like with code on Github!" While you intend the comparison to be a way to explain a lot with just a few words, in reality it might be interpreted all wrong, giving users entirely unsuitable expectations when checking it out.

So, please try to communicate clearly about the thing you have made using every day words. Good luck :)