In my installation of the Stack Exchange Android app, I found Documentation beta in the all sites list in which there is only one question saying "Welcome to Stack Overflow documentation Beta!". When I try to join the site, the app crashes.
But I cannot find it in the all sites list on the website. What is this site and why can't I join this site in the app and why can't I find it on the website?
I can't even find it on Area 51.