It says Private right in the name, but on launch it immediately phones home to GitHub and some VPSes.
Private from youtube as in you do not need a Google account
YouTube.com doesn't require an account either. What exactly is this buying us that you don't get from just opening the site in incognito mode?
But without account on youtube.com you cannot subscribe to channels. With FreeTube you can. And also it is open-source[1]