No worries mathiaspriebe, and no donations are necessary :)
For now, I don't want to take full ownership of the plugin (the original developer may return)... but I am making some tweaks that I think are useful. If you'd like to receive notifications of these, sign up to GitHub, and click "watch" on my code. You'll get an email if I introduce a new feature, and you can decide if it's useful to you.
This will be my approach for now. If the original plugin developer remains offline, then I'll look at making my "version" more official.
I am currently working on an enhancement, so that unauthorised users can be assigned to a different user role within WordPress. This will allow for more flexibility in choosing what unauthorised vs. authorised users can do.