Dribbble invites are rare, and so they should be as the site is only for the best designers. Any bad designers are simply ignored.
The Dribbble community is all about showcasing the best work. It's an exclusive network where designers can also acquire work from clients who are hiring, and that's usually why people want to get into the network.
However if you don't know anyone who is in the Dribbble network, it can be difficult to get an invite, even if you are a fantastic designer. And if you are a Dribbble member looking to invite someone, it can be difficult to find good designers.
Draft.im is a site that wants to solve the problem of getting invited to Dribbble and finding people to invite. The site is free to use. Designers who are looking for an invite can submit their work, including a link to their portfolio. A person with a Dribbble invite can look through any of the work and invite a person if they like what they're doing.
The site is a great way for designers to get into the network and for invites to be handed out to those who deserve it.