This is actually a clever way to spread the word. I only say this because it got me excited to sign up. By hanging the carrot of "being one of the first to be invited" you tap into the human psyche. You start a pseudo competition for who gets to be invited first. This abstract promise can be a powerful motivator for some, and you only need some to start spreading the word before the snowball effect.

Is there an open source code for this? I'd like to do this for my startup. It would be ideal if we could save time from having to build it.